A lot of guys get confused when it comes to this . Remember you are building a new car here not just altering one. You need to ensure that both the trans output shaft and the tailshaft are as close as you can get to being on the same angle, for the street 3 to 5 degrees is enough. Try this; take out your springs and support your chassis with a jack at your desired ride height then try the tailshaft through your expected range of travel. this will make sure that you dont have a bind situation as U joints only have a narrrow working plane. Also remember that the diff pinion will move up and down considerably more as the rear axle has more bias due to being a higher ratio unsprung weight compared to its original location. If you are running an E brake and I hope you do, it also will influence diff pinion angle movement. When I was a registration inspector with the ASRF' I inspected a real nice 41 Willys coupe and as part of the inspection a brake test was required all was fine on the service brakes but when the E brake was applied as it would in an emergency, the pinion nosed down and the tailshaft connected with the tailshaft safety loop and if it was kept on would have caused seriour damage, just something else to consider.
Good luck with your project
Cheers from Aus: Rob