Rear tailshaft length will be OK (after the lift) for normal driving but you will probably have driveline vibrations because of the angle - that's what the double carden joint will fix. I have no idea of price to get the tailshaft modified, you will need to talk to a driveshaft specialist.
At least you can keep driving around while the rear shaft is out getting modded, just put it in 4WD, lock the hubs and run around front wheel drive!

Tony