It will be the domed type and when installing you tap on the front of the dome so that it spreads out and seals. There will be a ledge inside the hole in the block that it will stop against. I like to use some sealer too. In my case, after the one on the front of the motor failed, the one in the rear did the same thing. They were old and rusting around the edge.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!