The best reference for the B6500/6700 on bitsavers will be: https://bitsavers.org/pdf/burroughs/LargeSystems/B6500/1058633_B6700_Reference_Manual_197205.pdf
The Handbook is useful, but more of a quick reference in a smaller form factor. Note that the B6500 and B6700 were the same machine. The B6500s that were first delivered to the field had many electrical and a few logic problems, and fixing them required swapping out the old processor cabinets for new ones. All existing customers received the new processors at no charge, ca 1971. Architecturally, the processors were the same, but Marketing decided to rename the system for reputational reasons. So in addition to the new processors, all of the existing sites received a box of new nameplates, which the Field Engineers had to go around the replace on all of the cabinets. I still have one of the original B6500 nameplates.
