Don’t sweat the drive shaft too much. The drive shafts are all two piece units to accommodate the steep angle from the back of the engine to the differential. The rear section of the drive shafts are within an inch of each other for the three tubes, 3-speed, 4-speed or automatic.The front section is about 31″ long for the 3-speed, about 20-1/2″ long for the 4-speed and about 25″ for the automatic transmission cars. Therefor, the 3-speed drive shaft is the longest used in any configuration. You only rework the front section of a driveshaft so you can keep the center bearing in the same location as original. A drive line shop can cut the 3-speed drive shaft front section tube to the needed length and weld back together for almost any transmission set-up. Cost to do this, from my experience, is less than $200 including a re-balance and you will not need any other parts.Attached is a pic of a front section that I had re-tubed.