1941-1954 3/4 ton trucks used a hybrid driveline... torquetube to carrier bearing then convetional driveshaft to the rear. No need to change that with a gear swap. However if swapping transmissions, the one piece driveshaft may be easier to fabricate.

Of course a transmission swap has it's own challenges on a 46. The transmission to bellhousing bolting pattern is different than the later chevy and gmc trucks. Most transmission swaps will involve using a modified 1948-1954 bellhousing. An adapter plate could also be used between the old bellhousing and a newer transmission.

I have plans of swapping out the non-syncro crash box in my 1940 gmc project to a fully syncroed nv4500 5 speed.