All parts needed to convert to 4-speed are specific to the 1962-1963 F-85 series of cars. The 1961 F-85 series was available with a 3 speed manual transmission or automatic. No 4 speeds in 1961. The factory 4-speed is a Borg-Warner T-10. It would be best if you could find an original 4-speed car that still has all the parts (good luck with that). A specific floorplan was used in 4-speed cars to allow space for the shifter. At the factory they cut the tunnel portion out around the transmission on the standard floor plan and welded in a new larger tunnel section. If you can’t find an original car I believe D & D Fabrications (aluminumv8,com) has a replica floor pan constructed in fiberglass if I’m not mistaken. You’d still have to source all the other stuff. You stated that the car is “beyond gone”…….it might not be worth going to all the trouble. There are members of this website who may have some of the things you need and they see this post.