I did the GT40 porting thing once. Wound up with almost $1k into them. Basically like taking $1k and lighting on fire honestly. No, they are not worth porting. They are ONLY worth it if you have a clean set you got for cheap and can just bolt on. I mean they are good heads for what they are, if you have a 93-95 Cobra with them you are light years ahead of a GT in rwhp and bolt on power gains but its not the same as a good set of aluminums. Not even close.
Now... as far as the performers... they are decent but they're pretty much a waste of money too. The only ones worth getting are the RPMs with the 2.02 intake valves and those will have issues clearing stock pistons. IMHO, if you have a 302 based motor and are looking for aluminum heads the CLEAR winner is the TFS Twisted Wedge heads. Yes AFRs are great too but the TFS make more power than the 165s without the potential clearance issues of the 185s and have the added benefit of being outstanding heads to work with from a porting perspective. There is a ton of "meat" on the TW 170s and they can be taken out by multiple shops to support even a 408 stroker no problem. Get the TW heads, get them once and never have to buy heads again unless you break them somehow.