Check out your pistons compared to these Wiseco PT042H3 pistons. They are the correct pistons for 67-69 Chevy DZ302. The compression height is probably different. Wiseco PT042H3 - Wiseco Pro Tru Forged Piston Kits - Overview - SummitRacing.com
. Expensive too! The 30-30 solid lifter cam(PN 3849346) was the cam used in the DZ302.