The most reasonably priced component used on the G4trc 1973 Usa Canada Seat/carrier ('74-'75) is the Cotter.
Some items from this specific schematic: Nut,10mm, Luggage Carrier, Key Set,#401, Washer-spring,6mm.
The Seat/carrier ('74-'75) is made up of components including this Seat Assembly,dual which is the most expensive.