If your .060 over 389 needs to be bored again you can go to.090 over and use .030 over pistons for a 400. Caution between 66 and 67 Pontiac changed valve angles so if you do this and use your 389 heads you may have a valve clearance problems depending on the cam you use. The plus is you can use newer style heads to get your compresion down so you can run pump gas. I've been through this and its a pain in the ass unless you do it right the first time, hope this helps.
|