Possible if they had a pile of 010 blocks left over- they quit casting then in '79 or '80, so to be in an '81 (Dec. '80 cast date), it would be a left over.
OP- do you have a carb? If yes, find the carb number stamped
onto the body
. If the intake is there, see what the cast date is on it, too. If there were exhaust manifolds, were they rams horns or logs?
The deal w/that CLY suffix is prolly that the engine is from a 1-ton or larger truck. The bigger trucks are not very well represented in the casting info from Mor Tec, etc. That could also explain why it was a 4-bolt 2-bbl.
I'd like to see what valves were in the heads- could be those big, 3/8" exhaust stems and might also have 1.72 intakes if they are correct for that engine and it was a truck.
Big trucks can have steel cranks so you might want to take a look to see what the parting line looks like- thin = cast, wide = forged, or look for a casting number on it.