[gsharapa]

I would agree it is mostly the head gasket but were the heads ported or C & C at all?

I had a 351 built with Brodix heads that were C & C from Brodix and when we fired up the motor to dyno it everything seemed fine for a couple of pulls. Then the HP dropped and we lost cyl pressure like you are explaining in your post.

Turned out the C & C job was incorrect on the Brodix heads and the intake and exhaust ports burned through on several of the cyl. If you take the intake off you can look in the ports and see if that happened or not. Hopefully just a head gasket.