I don't know anything about rear disc conversions or whether those perches might fit your frame.
Pressure shouldn't be an issue as much as volume, I would think.
U-joints shouldn't be any problem.
Ford used many conversion (b astard) U-joints over the years.
That word seems to hit the language filters, but that is what to ask for at a driveline shop.
Jim (AKA Princess Glitzhooter)
'87 F-250 460, 4V 0-80457s, Edelbrock Intake, Saginaw PS Pump, BW 1356 4x4, 4.10 10.25", 130A 3G Alt., PMGR starter, ZF-5, - Lil' Red
FTE Fraternity of Blue Max