Hello PC and CJ
I agree with Jack that the blue Sunbeam is the same base for the two and four stroke motor.
The orange / brown base Sunbeam, I believe the two stroke base was cast and then the centre
was machined out when the four stroke motor was used.
It's a lot cheaper making one metal die than two dies.
In pic S2 it shows the two stroke base with the four stroke casting built into the base.
Cheers
Max.
