the 4 gear cog box and 3.91's are about what i would consider the limit for a regularly street driven car so you're doing good there.
you just need to understand that it's going to have a narrow peaky power band is all.
you can get some compression by swapping heads and running a thinner headgasket, but those are kind of band-aids. the best solution is pistons and machine work. which means really, you should probably just get a 360.