Just because they are "newer" doesnt mean they are better.. Could have smaller valves, smaller/bigger combustion area etc... This all affects compression ratio and getting air in/out of your motor
E7s are everywhere cheap because the multitude of engines they came on had them taken off because they were so... uhmmm... "good".
Says who? You? E7s suck. They are not a performace head, period. Any posting work on them would work just as well on "Maverick" heads. BTW, there is no such thing as "Maverick" heads. This is the kind of deal you want on heads: http://www.tcstangs.com/forum/showthread.php?t=51981 You can get GT40 heads pretty reasonable too.
Back on topic Thread has deviated from the original question to a discussion of heads... 1) open the exhaust, 2-1/4 or 2-1/2" all the way, dualled, or dual with an X pipe. Lose the exhaust manifold and use AT LEAST a shorty header, if not full length tube headers. 2) better heads...the better...the better....GT40s are about the best iron heads you can get cheaply and without needing to do a bunch of work on them. Just clean them off and slap them on. Of course, porting won't hurt them either. 3) Better intake...the better...the better. Lots of arguing between the Torker289 (NOT Torker II) and an RPM Air Gap. Weind Stealth??? Of course, porting won't hurt either... 4) advance the timing and/or recurve the timing 5) better cam, lots of work but not too expensive, with very good benefit. 6) An aftermarket aluminum radiator won't necessarily improve the 302, but will allow you to run cooler which might boost HP, and it will keep a higher output 302 cooler after you start tacking on the HP boosters. 7) Nitrous 8) Lose some weight. (Might be good for YOU too, if you have a little extra to lose ) Drop the big bumpers if you can find small replacements. I will think of some more later. Hopefully, this will provide some non-head fodder for everyone to improve/debate upon.