Answers from the prior owner don't seem forthcoming just yet. Doing a little independent research, I've found that Curtis Novak offers 40mm & 44mm covers for his Mustang pickups, the latter fitting modern reissue pickguards made for the skinny puppies. That said... American Performer & Vintera bodies have different routings than the Player and Offset, from what I can tell (no switch, so all that wood is still present), including slightly different pickup location... also, deeper cuts since the Mustang pickups are taller.
Until I hear back, I'll have to assume the project involves some routing.
On the other hand, if the stock pickup is the same vintage-voiced split coil that's in my 50s Classic P, well, there's far worse pickups out there....