I am in the beginning stages of a teardown for a full restoration of a 1972 T120V and have noticed something peculiar with the seat latch, per the parts book and photos online, the 71/72 T120's used a clasp type latch over the previous version with the spring loaded pin type.
The low seat frame was introduced from serial number CG50414 during the 1972 production 'year' which is why the later low frame seat (and plunger etc.) isn't in the '72 parts book.
The low frame seat part number is F14599 (83-4599), however, UK/General export and US version seats had covers to suit the different width fuel tanks but both had the same part number.
For the 1973 model year, the seat hinges were moved to the left-
hand side with the plunger knob on the right.
If you were to order the 83-4786 seat listed in the '73 parts book it would be the left-hand hinged, right-hand catch seat, in the link, below. https://www.thebonnevilleshop.com/p...at-1973-77-twins-pn-83-4786-w-83-7065-w/