727 9 1/2" Street/Strip Converter

As far as I can tell, there is no problem using a big block 727 converter in a small block 727. The cast crank motors converter used external weights to balance, so that would be one exception and then the later 70's 727 had a lock up converter. Those seem to be the only exceptions.
Oh, there might be a little less stall behind the small block because of the torque difference.