I have a 1951 235 block with casting number 3692703. The Stovebolt casting page says it's a passenger powerglide. My head has the casting number 3835909. Two heads match with my block, the above mentioned 3835909 and casting 3835499. When I went change the head gasket, I noticed two water port holes on the head (between the second and third spark plug and fourth and fifth spark plug) that aren't on the head gasket or block. The whole setup is in a '46 2 ton, so I know many things have been swapped. My question is: is there a difference between the head with casting number 3835909 and 3835499? Is one meant for the truck block and one for the passenger block? I'm rebuilding the whole thing, so the new head gasket isn't due to gasket failure. What's the difference between engines equipped with powerglide and truck engines (besides the actual transmission itself). Thanks, guys...