The OE Vortec heads are bad about cracking. Yes port and polish will help, but there is more to it that that. The rocker arm studs are pressed in, and will need to be removed. The holes will need to be threaded and the screw in studs will need to be installed. Also the spring seats will need to be cut to allow for clearance for any cam larger that around 500, I think. They clam that the CPI will support around 400 HP, but from what I read, that is its limit, and you may not get that out of it. To make good power, you need to get fuel- air mix into the engine, and then exhaust out of you engine. As for a 383, yes those engines make good power, but again, the bigger the cylinder, and piston is, the more air and fuel it will need. The power in any engine is in the heads, and cam or fuel delivery, and then that needs to be able to exit the engine with out restrictions.