Prolly an easy answer for most but is there a particular casting number and a good source for GT-40 iron heads that will bolt onto my 65 289 block (C5AE).

Also is there any flow advantage to GT-40 iron heads over building my stock 65 289 heads while using my stock manifolds.

 

using your stock manifolds will hurt you pretty bad, but the 40's will run circles around the 289 heads. easy ID is the 3 casting lines on the ends of the heads. the 40p's have 4 lines, and regular 302 heads have no lines. i believe the 40's have a casting # of F3 and the 40P's start with F7

 

look for 96-97 explorer heads gt will also be cast into the head