FWIW, the stock 1978 heads have a water jacket in the exhaust port, IMO anybody that wants to 'port' these heads either doesn't know what they're in for or they just want to start sucking money out of your wallet. D5 heads pretty much suck and have no place in a performance build. if you want to stick with 2V heads get a set of pre 1975 castings and start from there. you can't remove the material from the exhaust port of a D5 casting or you'll hit water

don't believe the 4V's are too big fairytale that started when the chevy ragazines put too much cam and not enough gear on a 302 engine and the performance didn't make them tingle. cam duration, stall and gearing has to match the application