Hi there,

I came on this post by accident, looking for something else.
Hi Non-Fixie. Long time not see

Indeed this is a Plume Sport bottom bracket signature.
Lenman can ask the build details on Plume Sport, Anderlecht/Bruxelles | Forum Velo Retro Course (proboards.com) and will likely get this from the frame builder.

I personally believe that the 4 holes on bb are a later addition.
About Jan Weymans, having had several discussion with him (his version of dutch accent doesn't help for me but this is a belgian story), I already faced doubtfull memories.
Other frame details let me think that this "may" have been made by another belgian framing company to which, Plume Sport outsourced some production (to be confirmed or infirmed)

Anyway, not FAEMA related, nor Terryn, and extremely doubtfull on Weymans paternity
Despite of this, allways happy to learn of other belgian collectors