How hard is it to switch from a slip yoke to a fixed yoke like on a bronco
BW1356 comes with 6 (or maybe more) rear extension housings & corresponding output shafts. You want to replace the slip joint extension (with or without speedometer drive) with the corresponding fixed yoke one.
You will need the appropriate extension housing. Then you can either do:
a hack and tap - which can be completed in vehicle, but there really aren't any kits for so you would need to source the appropriate bolt on your own.
or,
Remove the rear cover/disassemble to remove the slip yoke output shaft and install the fixed yoke output shaft in its place. Button everything back up again, fill with oil and you're rolling.
Given BW1356 really doesn't fit in RBV without mods, not surprising that knowledge is limited on this site.