I'm sure you've already been told it is a bog standard 6E Villiers unit. This is a 3 speed 197cc beastie and was the largest motorcycle power unit they made at the time. Made from 1949-1953.
Yes, the first three digits, 996. do identify who the engine was made for but much of the records have been lost and 996 is among the lost. The late Roy Bacon compiled the major list that most of us Villiers nuts refer to and I've amused myself adding to it over the years but 996 does not appear in either his or my listings.
From the point of view of operation and maintenance the number is irrelevant. There are minor difference between the first and last 6E as Villiers tweaked the design over the years but essentially all 6E's are the same regardless of what they were fitted to.
Spares are reasonably plentiful and luckily they are not an attractive engine to the pre-65 trial crowd so they aren't mauled about. They find the 3 speed gearbox a handicap. Personally I'd put it back in the Tiger Cub frame and use it as a neat little stylish road bike. The Tiger Cub was always a pretty little bike but with an engine not quite up to the job. The 6E is a very good unit but often ended up in some rather dull bikes. If done properly it'd be a very happy marriage and you can always truthfully tell the nutters that it is as you found it.
Let us know what you do.
