building a kz1300

can you fit a model A enginge into a model B frame they are both 1980

I would say yes.

Yes, same motor in the A model and the B model.

It would need to be an A1 or A2 motor (79 or 80) to hook straight up to the ignitor box on the B2 loom

Not sure how much value my post will be since it was such a long time ago and I can't remember the years but I blew the crank on my original 79 KZ1300. As it happened, I found a low mileage engine from a wrecker for not much more than the cost of a new crank and bearings. I can't remember the year of the donor bike but the motor went into the 79 frame just fine and everything hooked up as it should. The problem was the engine covers: I wanted to keep my original covers and swap them on to the donor motor - I think but can't remember for sure - the donor motor covers may have been chromed. In any case, my covers did not fit (that may be a clue to the year of the donor motor) and I had to go back to the wrecker to get the engine covers for the donor.