You are right about the instrumentation, although I initially want 2 pressure gauges.
The only weather shielding was some black paint, more to make the instrument semi invisible.
The blue wire is indeed a temporary lead to attach the scope.
At this point, cutting the tach open was the only solution, I had to see how it is made, and since it would otherwise be scrap, I might as well see if I could learn something by peeking inside.

The speedo cable. Advised by some armchair specialist on a Facebook Savage group, I purchased a cable For the GT500, and although it mated to the spedometer end, it was both too short and did not mate to the engine end. So I mounted the original cable to the engine, the GT500 cable to the instrument, and zip tied them together where they overlapped under the tank.
Then I cut them both with the angle grinder and cut the outher sheaths another 25mm back. Thus there is 25mm inner cable protruding from each cable.
I now take 125mm lengths of 20mm shrink wrap (with glue), feed them on to the cables, and stuff them as far away from the joint as convenient, so that they don't start to shrink when the soldering takes place. I also feed a brass tube, could be any metal, really, and push it up the cable.
Before all this, clean the inside cable with gasoline, heat it with a torch, blow it free from oil, rub it with emery cloth to a shine, and tin it using methods known by plumbers.
Then join the parts, so that the tinned cable ends are introduced into the copper tube, which is also tinned on the inside.
Finally heat all 3 members and apply a bit more tin to the solder joint.
After this, slide the brass tube over the joint, and shrink the wraps down from each side, so that they overjap each other, the brass tube and each their own cable end.
Hope this helps.

I do not ride a lot, but have now covered 500 miles since the rebuild, changed oil once and tried to feel at ease with the clonking sound from the engine.
To recap: engine sounds fine when I accellerate, and during decelleration. But above 3.5K rpm, if I ease off the throttle the engine emits a clonking sound, which I assume to origin from a too large clearance between piston and cylinder. If I ease the throttle off completely, so that engine braking occours, then the clonking stops. I am on the brink of tearing the engine apart to see if something serious is going on inside, with the cylinder, but hesitate due to other things I have promissed to do for the missus, build a henhouse etc.
Today I took it for a spin, 50miles each way, and did a couple of WOT pulls from 3.5k to 5.5k in top gear. I have not got my gopro mounted yet, so I counted seconds like I did in my skydiving days: 1thousand, 2thousand, 3thousand etc. and it did 3.5k to 5.5k in 6-7 seconds. We will see when I get the gopro mounted. It keeps going to 6.5k and it hits 90mph at that revolutions, and it would go further if not for my recent vow to nottake it further. So it would appear I have to get the Kawasaki pulley set mounted if I want go beyond the ton.
I probably should have let the engine run in more gently, but the sound from the clonk was there from start one after the rebuild.
Perhaps this is just how a hotrod sounds, not that it has to, but might in some cases. like this.
No oil on the engine outside, no smoke from the exhaust, no oil consumption.
And on this 100 miles trip, mostly cruising at 50mph, but with those 3 WOT pulls to 90MPH, it used 6 liters of gas. That is 71 MPH, which sounds pretty sweet.
I have not covered a distance with that mileage since I drove the VW LUPO 3L diesel.
The homemade cam chain tightener was installed with near zero backlash.
I have bought the gasket for the generator side cover, so I can check if the flywheel has come loose, and I have already checked the primary transmission without finding anything obviously wrong there.

As should be obvious, I am not dissatisfied with the bike, it pulls good and strong. But I am also quite embarrassed by the sound it makes, because I feel it could be avoided, and perhaps it shows I screwed up. But how is the big question.
Perhaps the gopro can record the sound.

This is the noise my loose flywheel made.  It seemed to be most pronounced when I throttled up.  Loud metallic clacking.

https://www.youtube.com/shorts/KUhN_OHQhmo

That's some sweet fuel economy Finn.  How is the hi-flow muffler working out?

You were close DBM. Intruder speedometer but the cable is the tach cable from a 70's GT750. It is a perfect fit on my bike. If you want to stay with the stock look, unwrap the chrome spiral from the stock speedo cable and wrap it back on the GT750 cable.