There are many variations of the 14 bolt FF gov-loc. The early ones are from roughly 73-90, they are small journal and guts will not interchange with 91-up cases. The early 70's versions had a larger governor and latchet but IIRC can be interchanged with small governor early design.
Later versions, 91-up? had large journal spiders, the spiders are the same as 14B SF. there were case variations and at least two spacer designs between the side gears, two thrust blocks with a shim or a ground cylindrical spacer.
Do you know if you have a 90-back unit or 91-up?