First off 4V heads will kill those heads out of the box, only after you put in $$$$ are they good & you have to run their intake = more $$$Do you need an iron 4V or aftermarket head to make 375HP? No, I never implied anything close to that. My advice was about time and money.
Iron 2Vs have a poor intake short turn radius that isn't easy for a first time porter to get right. Porting is very time consuming...not bad for a DIY project if you have the tools and determination but I wouldn't pay a professional to work on that type of head.
The open chambers are a problem for getting decent compression with a flat top piston. Figure about 9.25:1 tops for a zero decked, stock stroke engine.
Now figure out what you have to spend at a machine shop to get the heads reconditioned. Disassembly, cleaning, magnaflux, resurfacing, new guides, hardened seats, valve job, machining for screw in studs, etc?
I'm not saying it will need all these things...it's just good to be aware of expenses that may be needed to make an old head like new before comparing price to an aftermarket bare head.
I don't think I have to go into the obvious advantages of new technology.
Aus Ford Parts - Aussie 351 Cleveland Specialists
CHI & AFD always do dyno runs against iron heads using a smogged down stock non flowing intake. Put on a Holley or Blue thunder or something else then we will compare.
After market heads WILL make more power but only after you spend alot more money