Console or column shift?
If you go with console you can keep your existing steering column. If you do console you obviously need the console, shifter and floor pan section.
You will also need transmission lines and a radiator with a trans cooler if yours does not already have one.
Im not sure but I think the 4spd and 727 tailshafts are the same so driveshaft should be the same.
727 will require a shorter driveshaft, but the yokes should be the same.
The 904 can use the same length driveshaft, but now with a smaller yoke,
If you cut out the 4-speed hump, you'll need a front carpet,
And you may wish to swap out the two-pedal system for the one larger brake pedal
and a bit of rewiring for the reverse lamps and Nss
You can use a stand alone trans cooler if you don’t want to change out radiator at this time. Or any time for that matter.
Unless you already have a 727, don’t discount a 904, less parasitic drag, lighter weight, & can be built to handle just about anything.