Woodrup frame no. location??

[converse320]

I'm trying to find a frame number on a Woodrup - I'm guessing its 60s. Nervex lugs I think. There are numbers on the bottom bracket, but I think these are Nervex numbers as they don't correspond to any frame numbers I've seen for these bikes.
The BB has:

33104J1

and then below it a "cross" of numerals, with,

9-2 running horizontally, and 3 0 running vertically through the 9-2

It has been powder coated, so any help on where to scrape would be useful. Worst case I guess I'll have to have a look at the steerer.

 

[Midlife]

I had an early Woodrup (had it in the early 70's and it was second hand then) and I'm sure it was on the bottom bracket but on the part of the lugwork to which the chainstay was attached....

Shaun