Well I decided to open it up further. Mine has an 030 at 33Mhz with an FPU. Good! So that is spec for a IIvx. Wonder why Apple advertised it at 32MHz?
So my guess is -A came out for IIvx. Then -B was a revision which was used for the:
IIvx (32mhz 030 with FPU) (replaced -A board)
IIvi (16Mhz with no FPU)
Performa 600 (32mhz with no FPU)
The ones with no FPU seem to have had a socket to add one. So this makes more sense, -B might be a more "universal" board to accommodate the 16Mhz 030?