73 engine question

I have a 70 GTO with a 73 400. The 73's are rated at only 230 bhp which is an insult to a 70. I was wondering what can be done to the engine to bring the horsepower back up to a respectable number. Is the emission equipment that can be taken off? What can be done? Thanks

There could be alot of things, you are going to have to do some research. Things that quickly come to mind for me are valve sizes (73 are probably smaller than the older heads), cam lift and duration (again, maybe lobed down a bit). I am again guessing that bore and stroke may be the same, but pistons may be different...flat top, dished, etc. Emissions certainly didn't hit hard in 73, but it was about that time when the EPA was gearing up.

I have a 69 XH engine that has the 62 heads on it with a weiand intake and holley carb w/ headers that I am willing to part with. I was told it has a mild cam, but have never verified. I am guessing that with this combination is is at around 365 HP. It runs, but has been sitting around.