The brown spects turned out to be rust. We tore the block apart , on acount of some unpleasent noises, and found two cylinders with light scoring. We will bore it out 20 thousands. Both exhaust manifolds are cracked and I'm wondering about using sanderson cast headers . Wouldn't like to buy factory and have them crack. Any opinions out there? I'm also wondering what compression ratio to seek since I have to buy new pistons. The cam will be chosen for low end power. Ant suggestions? Many thanks for the help.