I had the same BB short shaft with a 3 5/8 u-joint.

FYI..truck pullers want that yoke to go bigger drive shafts

727 output spline is the same for a small 6270 joint.

I removed mine and slide a small yoke on from a SB 727 short shaft trans from a MH.

that trans will also have the HD 4 gear planetary and HD servos.

I have bolted a SB shorty in a 68 dart and the bolt on yoke clears the cross member and only needs a slip yoke change. I will wager the BB will fit a car also with a shaft change.