My first thought to give it power is put it on alky...but, just not feasible for trails.
When I had my 85, it was dune ported, AAEN pipe, big 39mm carb, no air box, real short gearing (went from 1 to 5 RIGHT NOW)...
Don't take this the wrong way...but, I think you'll get the most power out of that bike if you let a seasoned vet do the porting.
It's gonna be a fun bike to ride, and even though it's older than that banshee design, you're going to find it handles night and day better than a shee. I loved mine.
It's gonna be quick...just not fast.
You could push the limit with some compression (which you have...you could go more) and porting...but, the tranny's on those weren't the strongest...plus, you want it reliable.
Hard to have it real fast yet keep it reliable....
LT500 motors had a bunch of problems too. But, dr. q on planet sand seems to have perfected that motors inherent faults....they are getting harder and harder to find at a reasonable price...though.
I'd just put it together and ride it. It's gonna be fun...just not a rocket!