The 308's are open chambered so they'd be more than 60 ish CC's but they are the best OE open chambered iron heads but they'd be no quench. I'd think you get some 302's into the 70's & iirc they are 1.78" intakes & 1.88's with some good porting is a good plan for 302's. I have a set just ain't done anything with them yet