[frnkeore]

The reason for the late heads, is that on it's last rebuild, they put domed piston in.

The valves are just stuck open. You can probably tap most of them back down.

As for main bearings, you'll have to pull a main bearing cap and check for inserts.

Check to see if there is a plate (each side) on the front of the block, where the WP would go on the later blocks. You could have a '38 style, 21 stud block.

My '35 truck engine had a late block replacement. Same heads and pistons as yours.