I thought the Mk of a VIlliers was the cc's

12=120
20=200
25=250

etc.

The later ones its a bit different. 412 is 120, 425 is 250 and so on.

The ouput on the 4** is about half way between the std motor and the HS version.

Dont quote me, im no expert, thats just what i thought i had worked out with what little looking into it ive done.