I agree with banshee regarding swaps. I have 68 HT original 4 spd car (Missing WZ block). Currently have a 400 in with the 16's believe they are original. i had a set of 48's which is didnt seem to think they ran any better than the 670 or 16's in my combo. I have a 67 ragtop YT block, PX trans, 3.08 gears, Q-Jet. Rebuilt it with the 670 head and got it to run really good. I run long branch with 2.5 exhaust. less hassle than headers if your going to drive it alot. have and good luck.