I've never thought about it until now, but I wonder if the tabs on the transmission that you used for the fixture attaching points are in the same place on both big and small block 727's? I would think that they would be since the cases between the 2 are the same, aft of the bellhousing.
The tabs near the tail housing are the same, but at the bellhousing, the small block tabs are wider by about 2 inches. The dimension front to rear is the same between the two.