Oil bath air cleaner question

Hi, I am going back to stock 1600tp.
I want to use a metal VW oil bath air cleaner, and just missed out on a dual entry one on ebay.

I am sure there were a few iterations of these over the years,
What year model would these be from? any other suggestions welcome.

Thanks.

Here's an old article from the Club VW magazine, about how the pre-heats work on various models of air cleaners:

http://www.clubvw.org.au/oldart017#fue06