Hi Commando_Al,
my first piece of advice would be...
see if you can squeeze a DR750 engine in the frame, that engine is definitely powerful!
...or an 800 for that matter...
Else, do some
healthy head porting, replace japanese carb for proper Dell'Orto (off a wrecked italian bike) or even a Bing (off a BMW) I have never worked on a jap carb but if most classic tuners use Dell'Ortos on classic cars&bikes (European ones of course) then there must be a reason. And a K&N or similar filter.
Exhaust: ask around on track days and see what the racers prefer, it's a matter of backpressure else the bike will burp all over the place but will actually be slower.
Change the belt drive to chain so you can play around with the final drive ratio, even adding or subtracting just one tooth from the front sprocket can change the ''feel''.
Move the footpegs a little more to the rear, improves handling in tight bends considerably.
Try to ensure tire size is as similar as possible front&rear, it helps ''feel'' the bike. Also, good grippy ''wet weather'' tires, any old man can ride on semislicks... until it gets a little cloudy or dewy in the morning...
Make the bike lighter... stop eating all those burgers and shave off a few pounds
(that's the advice they gave ME!!!)
(sorry, no FAT smiley here)
Maurizio