Crown Lynn lamp base 538

I have a white lamp base, which appears to have been molded from a modified urn mold. The base measures 205mm to the rim, where the urn would have finished, and 270mm to the top of the molding. The base is square with chamfered corners, width across base is 110mm. Diameter at rim (widest point) is 140mm.
The finish is satin white and the base stamp a blue/green crown and the words "Crown Lynn New Zealand". This would indicate a date of 1955+.
I thought I had the matching urn but cannot find it. The same design in a larger size is numbered "2077".
I have yet to see a similar lamp base, although I have seen many examples of the urn, in at least 2 sizes. I think I have only seen one other Crown Lynn lamp base (different design).
(picture added)
Any information about Crown Lynn lamp bases would be appreciated.

Looking forward to seeing your lampbase Jeremy!
We have a couple in the Crown Lynn Shapes in General Gallery.
432 and 538
the latter has an urn shape look about it....
there are also drawings from the Auckland Museum of 531 and 532 lampbases.

Thanks Ev. I had already looked thru the shapes but missed it. My lamp appears to be a 538, and also appears to have the same electrical fitting as that shown. Any further information would be great.