Probably easiest before... since the original forward bushing in the torque tube is a bit easier to pull, and driving the new bushing assembly in straight will be a bit easier.
But If you have the driveshaft out, removing the rearward bearing and (what's left of) the original seal is fairly easy, so as an option, you can replace those with original style parts as opposed to installing the OKie bushing assembly (so named because the original inventor assigned the patent to National Machine Works in Oklahoma City).
On the plus side, for the OKie bushing - the seal will ride in a different spot on the driveshaft, so may have a better sealing surface. The down side of installing the OKie bushing, vs OE-style bushings and seal, is that if the OKie assembly ever needs to come out, it's a bear of a job. Flip a coin...
Maybe it's just me, but I get a kick out of seeing the old patents on clever inventions from the past that have stood the test of time. Image is from the original patent filing. You can find the full patent (and a few related later updates) by searching with the patent number, 2403520 and National Machine Works, or the inventor's name, Theodore Gerner.