[42merc]

Looking at the carb, water pumps, red oil filter & the bell housing next to it, I say it was plugged into a truck.
Scrape a clean spot on the block, if there is lite green paint that matches the heads, it's a good chance it is a Mercury.
The motor not turning & unknown condition of the block, the only valuable part is the 4" crank.

Edit: The bell hsg is 53 truck - The water pumps are '48 - '52 truck