Powerpack heads dont flow worth a s*** and are pretty much worthless except for mabey a nostalgia hotrodder. The double hump heads flow pretty decent for being a stock head but you would be much better off finding a set of vortec heads which flow 10x better than the double humps.
Double humps also dont have any acc holes soo you are limited there too.
I'm going to run a set of double humps for now because I have a set in amazing condition with 2.02/1.6 valves and all Im going to do it clean up some of the casting burrs and throw a set of roller tip rockers on them. These heads will flow much better than the smog 305 heads i'm running now.
If I were you I'd save up for a set of good aftermarket heads.
Slap a set of 1.5/1.6 roller rockers on these edelbrock heads
http://www.summitracing.com/parts/EDL-5073/ and you could really unleash that 327 for about $1000 thats a killer deal!