OK, here is what I know. The drive tube assemblies can be swapped out between units with no issue. The innards on the early HT101 and HT70/75 are different than the late 101 and 131. If you have an earlier 101, you may have the early style telescoping shaft. I have recently been to school on these, but I had it mastered quite a while before I went to that. You will find a black greasy MESS inside of the tube. While you can grease the bearings if you like, you should not grease the star spline where it slides in and out. There are two ribs inside the tube, and they are supposed to be there. They help keep the bearing blocks where there are supposed to be. There are two long springs, and two sliding bearings inside. These springs keep the bearings evenly spaced wether the tube is extended or not. The early lower tube assy had an issue with the circlip sliding out of place if people got to slamming the tube in and out. The later design bearing solved that. Just take your time, and keep track of how it came apart. If you get jammed up :eek2: post back, and we can get you straightened out.
As for the gearhead end, they will all bolt on to each other. There are differences. Some have a slip-clutch on the drive sprocket, and some do not. I think only the HT70 had the direct drive. The other ones have beville washers that hold pressure on the sprocket. If the chain binds to where the shaft might be bent, the sprocket is designed to slip. Also, I have been told that there are two different gear ratios for the gearset.
Good luck. You will be fine.