You'll notice improvement - but not from the cam, rather the heads. As you've described what you currently have, you're over carbureted. The heads will definitely breath better but not knowing the piston configuration, a new cam would a crap shoot. Put the heads on using .028 head gaskets (GM part 10105117) and you'll be pleasantly surprised. Drive it like you stole it for six months and when you're ready to do some serious work, i.e., pull the engine - let's talk some real specifics and we can help you build a beast - or - you can call Pat and he will build you a monster that will introduce you and your friends to God (and result in a dry cleaning bill for your shorts!) the first time you find wide open throttle.

Have Fun,
Glenn