I've been told that they made the whole gun (they had the skills, facilities, and people to do it). But I would guess that it wasn't the case all the time. I may be wrong, though.
Regarding value, those Westleys sidelocks have to be taken on a gun-by-gun basis. Some stink and some are great, regardless of who actually made them.
But even the best ones by ABAS sell below London best prices. The quality's there--100%--but not the brand recognition and exclusivity that pushes stuff into the top prices.
That's what I've seen, anyway.
Do you have any pics of the gun? I would love to check it out.
Thanks
OWD