Quality bass. I had a GWB35 and that was pretty damned good, so I always fancied a 'full fat' one, but other basses came calling (as they do). A photo of the buckle rash would be welcome, as you have piqued my interest.
The sound from that seems to sit perfectly so I'm guessing the new one will do the same (plus you have the vintage switch option too). If your singer doesn't like that one, tw@t him on the head with it.
I did this with my old Roscoe Beck signature. I raided the tool box and reamed out a washer I already had for bespoke fit. The problem I found was that getting the right hole diameter for the thread, led to the flange being too big to fit in the packet. Thus the reamed out, smaller washer.
Worked a treat BTW.