Can anyone explain the Villiers engine number system, and what model Victas the number sequences started and finished on?

I'm trying to work out what model Victa mowers the following engine numbers came off:

Cylinder # 3812 B6698
Crank case # 402X 45 169

Cylinder # G3095?
Crank case # 407X 29 055

Crank# 764 55
65

Crank # 816
21 354


The top one has a brass pulley, the second a alloy pulley painted red.

As usual, any help much appreciated!