3B toothed pulley

[Ed Kellock]

Mine is cracked from the accident. I got one off an MC engine at a
junkyard. Later it was stated that it won't work on the 3B. I compared the
two and they appear to be the same. I didn't count teeth or actually
measure diameter, but the teeth appear to line up and have the same shape.
It was from an MC2 engine so it would use a super torque belt also.

If the really are incompatible, what am I missing?

Thanks!