An unknown engine , even for free is not worth the time to install it.
There will be few parts , after you finally figure out where it came from.
If you displacement trawler power look at an International DT360 or DT 466.
These come from skool buses and since they are free , are seldom recovered after a brand new bus crashes.
At very low prices at the wreckers , why bother with an unknown ancient engine?
If it WERE a 6-71 , I would say go for it .
The international DT 360 and 466 are available with electric injection , or on the older engines mechanical injection.
SAE bellhousing , so a Twin Disc will bolt up.