Geoff,
Probably the same Ford transmission as in my car. I have not had a chance to drive it any great distances, but so far Trans is smooth and quiet.
Clutch cable replacement was a major pain. Apparently the Clutch Lever on the tranny was too close to the fiberglass cowling and when somebody tried to disengage it tore a small hole in the cowling and destroyed the cable.
I just asked the original owner for the stats and what whas actually done in the rebuild of the Mustang II V6. Car only has a total of 12K miles on it. I’m actually very happy with the power and was frankly surprised at the original “advertised” HP of the V6. Also important to note that the original 1974 V6 apparently had a significant amount of HP robbing emmisions stuff installed. Mine has none. Sorry to all of you “green” fanatics, but it’s just one little car 
Rich