holy shit....80-90hp.....without spending alot of money....
honestly to get those your going to have to work some magic with porting and exhuast combos. your gonna need to be in the 4mil crank area also. and now your talking replacing the crank, different pistons, port work to match the 4mil, bigger carbs, blah blah blah......... and RACE GAS. and it MAY pull from mid to top nicely.....but low is gonna be kinda hurt from all the work.
NOW.....if your trying to get 80-90hp and want it to pull all the way from the low then i would suggest contacting a site sponsor and talking to them about a 4mil serval. The serval cylinders are known for pulling all the way from low to the top top end and also make 80+ hp on PUMP GAS.