dumb question #1: How do I tell if I've got a 283 and not some other small block without taking the engine apart?

Dumb question #2:The casting date on the front of my block say "F041IM". I believe that means it's a 1961 engine but I'm not sure. I couldn't find any other numbers stamped in front of the right cylinder head. Where would I find the ID number of the engine?

Dumb question #3: The reason I question whether the enigine is a 283 is because of the oil filter. I always thought that all 283's came with a canister type filter. I've seen oil filter adapters that allow a modern spin-on filter to be used, but the ones I've seen come with an adapter plate with an O ring to seal it to the original location and 4 bolts to hold it in place. My motor has a threaded hollow shaft screwed in where the canister bolt would normally go. The shaft is held in by a cheap "tin" hex nut. Is this some kind of homemade adapter?
The reason I ask this question is that I've got a leak somewhere at the rear of my motor. I'd hate to pull the motor to do a rear main seal if my problem is only an oil filter.

Any help would be greatly appreciated.