I have a 81 XV920R with a XVS 1100 crank, rods, cylinders and heads.  It has JE 10.6/1 pistons, Keihin FCR41 carbs and a MAC 2 into 1 exhaust with a Supertrap Universal silencer with a 2.5 inch straight through baffle.  It dyno's 90.7 horsepower at 8400 rpm.   I am looking to get more out of it.  I am using WEB cams with .498 inch lift.  The cam manufacturer won't release cam specs because they are custom made for Pacific Coast Cycle.  Pacific Coast Cycle does not know the specs or won't release them.  I think the duration is around 260 degrees.  Can you recommend cams which you have had good results with?

I think, your Mac 2-1 is one problem. The capacity is too small.
Make a photo from your bike, maybe i can say more.
Is the 90 hp on the rear wheel, or at the clutch?
Greetings S.