The CBM 128-80 high-profile B Series computer was never sold as "B700" in the USA, although a few low-profile B128-80's were sold as B500's.
Hi-profile systems with a motherboard P/N 8256068 (without the -1 or -4) were made about the same time as the B500 was produced so unofficially you could call these systems "B700's".
Anyway, I was asked to post some pictures of the motherboard, there is no reference to the earlier version elsewhere that I can find. Here you go:
NOTE: If I am wrong about this, kindly advise...this is info I got from an ex Commodore repair tech, I am going with his authority on the subject.