which engine do I have?

[jeffbcn]

Greetings,
Newbie here, first post. I recently purchased a 47 chevy thriftmaster. I love this truck already. I'm trying to find out which engine I have. It has been halfway converted to 12 volt. The casted number on the head is 3836850. The serial number on the block is 24768er cal. The engine has no oil filter.
I have done some research. It should have a 216 but the head number comes back as a 261 from 55 to 62. Since it has no oil filter I assume it could be 55 to 57.
The engine serial number seems untraceable. I can't find that number anywhere.
I did use the search option and followed to the mentioned sites. Still nothing.
I have no history on this truck and really want to know. Any suggestions?