[Ross F-1]

I don't think it's a choice to use the F-1 frame with the 4-sp out of the F-3. The F-3 has a different crossmember and therefore a different rear bearing retainer/trans mount. You could swap it to the F-1 style 4-sp retainer/mount, but honestly I would hate to be in traffic with the non-synchro trans. There are plenty of '48-'50 3-sp floor shift trannies around.

Do you get titles for both trucks?