[unruhjonny]

My guess is that this is from a Lemans;
I believe that for 1972-1974, outside of trucks, these were mostly found in the A-bodies - but I am unclear on which (if any) Regals or Cutlasses could receive these.

Keep in mind that the 1973 Lemans was the basis for that year's GTO.

I have 1972 and 1973 "Accessorizers";
Both of these show that the 6 cylinder and 350 came standard with the Saginaw, while the 'M13' was available with the 350 & 400 in everything except the station wagon.
It also says that the 'M13' was included with the GTO & GT options.

Can I ask if this is an "A" or "B" gear set?

I understand that normally the floor shifted Muncie three speeds were "B" gear sets, but I have read that some "A" gear set transmissions may have been assembled with a tail housing for a floor shifter... but info on these transmissions is rather spotty.