I pulled the flywheel off of my spare engine, which I thought was a 1985. The flywheel appears to be a 1981-82 flywheel, weighs around 23 pounds, but only has a '2' cast into the engine side, rather than the '21' that Mazdatrix says it should (see pictures).

Cast-in '2'

Engine side

Transmission side


I'm fairly certain that it is a 1981-1982 flywheel, but I wanted to check if there is some odd-ball Canada-only flywheel this could be that means I won't be able to put it on my current engine (which has a 1979 boat anchor) without throwing off the balance.

Also, is it worth pulling off my front cover to replace the front counterweight with the 1981 one, or would the gain be minimal?