I wonder what caused the original piston/bore failure...could it have been related to a fuel/air mixture issue?

Was the stock air filter and air box already gone before you started the bike rescue/rebuild?

I really can't explain all your problems - the stock muffler is restrictive....but not so much that it should make the bike run so poorly or require such big jets.  Same for the air filter......it doesn't make sense that it is causing such a problem.  The replacement of the stock piston with a higher compression Wiseco and/or the increase from 94mm to 95mm really doesn't upset the jetting much at all.......the additional airflow through the carb isn't very significant - and it doesn't require drastic changes in carb jetting.

I would suggest you go to a setup that we know works - the stock airbox with a paper filter.....and DYNA muffler - and since you are so close to sea level a #152.5 main, #52.5 pilot and 2 washers on the needle.  If that doesn't allow the bike to run well - you have something else wrong (cam timing, leaky valve, air leak, fuel flow, etc).

The rat chewed edge of the piston is from over heating, the top ring expands and the ends jam together ,there is no more room for the ring to expand so it pushed up until the top edge of the piston broke away. Doing 75 mph with less than 200 miles on the piston could easily have generated that level of heat. but who would do such a thing?

P.S. Shrulk is running a large air filter 155 main and no duct tape.You need a Dyna or similar muffler ,and you'll also be able to retire your duct tape.

I don't know what is going on with your carb/jetting etc.

My procedure for jetting a carb is to take and educated guess on where to start with jetting.  Then I start the bike up and set the idle fuel screw so the bike will run.....then go for a short ride to get the bike fully warmed.  Then I do a fine tuning on the idle fuel screw with the idle set low (around 800 rpm), as it allows the screw to be set while the slide/needle is fully closed - if you have to open the screw more than 2.5 turns the pilot jet is too small - if you can turn the screw in less than 1 turn and the engine still runs smoothly...then the jet is too big.  (I don't change the pilot jet yet as I still have to see what the main jet is doing).  Then bump the idle speed back up to 1,100 rpm.

The next step is to go for a ride and find a long steep hill, and get the bike in high gear and open the throttle wide open.....and see how it runs.  If it runs smoothly.....I then pay attention to what happens when you begin to roll off the throttle - if it seems to accelerate just slightly that means the main jet is too big....if it seems to hesitate the main jet is too small.

Then go back to the shop and let the bike cool down a bit, and then make changes to the pilot and main jet as needed.  I do something that may not seem worthwhile - but it makes me feel a lot better.  I keep increasing the size of the main jet until I reach a point where it is obvious the main is too big - then I back off one or two sizes.  When the main is too big you can hear the change in the exhaust sound as the engine will "blubber" a bit, and it doesn't pull as smoothly as it does with the smaller jets.

The last thing I do is work on the needle spacers.  With very light acceleration and a barely open throttle - the bike should accelerate smoothly.  Ride the bike as if you were in a school zone or riding with the police (or your mom) watching you.......very light throttle settings.  I start with 3 washers and if there is a hesitation/surging at light throttle settings - then I remove 1 washer and generally 2 washers will be just right.

If you have other mechanical/fuel flow/exhaust/intake issues - it may be impossible to get the jetting correct.

"The best result comes when we realize that an engine is basically an air pump. Air is pumped in and out and there are problems when one side or the other is RESTRICTED. Balance and flow is our objective, unless you are NOT trying to make more horsepower! "
        You have restricted your intake to balance the flow of your restricted exhaust. Take the duct tape off your air cleaner, grab a 5/16 drill bit and go out and drill 3 to 5 more holes in the rear of your muffler test ride after each hole drilled .If that isn't better , move to a larger drill and again test ride after redrilling each hole, one at a time.When you see any improvement ,it may be time to retune the carb. It 's time you realized the full potential of your motor which should give you a top speed in the 90's , and run smooth at any rpm.

Christo 13T,  the plate on the side of the carb ,with the three small screws is an enrichment valve that senses high vacuum in the intake passage down stream of the carb , and opens to add fuel to the intake track only when you close the throttle all the way to keep the motor running until it coasts down to idle or you reopen the throttle and has nothing to do with the operation of your stock petcock, nor does it open at all at steady speeds. the petcock draws it vacuum from the large passage inline with the nipple that the hose connects to at the carb  that is also down stream from the butterfly valve in the carb. 70 in third gear, really ? did you forget to shift or do you think running the bike past redline is cool?

Redline for the motor is 6500 rpm ,you may have been at 6600 ,you wouldn't have hurt the motor but I wouldn't make it a habit. you should remove the tape from the air cleaner ,it may be causing your motor to run to rich (bog) and that may be the reason for your hesitation . I'd do that first before trying to adjust the carb. Anything you apply to the side to lube it may make things worse, you can check the bore ,but I'd just make sure it and the slide are clean.

Here is the link for the video of it in its current condition.

https://youtu.be/IG14tFiji6w

The weather has been nice the past couple of days so I have spent some more time in the saddle and have some observations.

It is now more "streetable" than it ever has been. Smooth acceleration through all the gears. Acceptable, predictable, on demand afterfiring on decel... I get one crisp afterfire snap if I let the throttle close all the way during quick shifts...  I may have to try to get a video of it vs trying to explain it.

It makes it to 80 with no problem. I suspect when I do get it out on the nicer long straight pavement I will see what it really tops out at. Might pull off the windscreen and go see what she can do today. Very little wind this morning, hope it stays that way lol.