Get to that point and then deal with it, that's a minor issue and a long way off.
I had no problems measuring and speccing the driveshafts I had made for my truck, it was actually fun. The Spicer manuals are quite helpful.
If you're uncomfortable figuring it out yourself then the driveshaft will be the least of your worries on the project you have planned. Or by the time you get to the driveshaft you might have a good handle on what's going on and it won't be the worry you think it is now.
