Ali ,

the shift axle is not interchangeable, that is what Sepp means I think, they differ in length !

So ,
Axles with gears from BT1100, forks from BT1100, final drive gear from XV1000 TR1, small axle for forks and shift axle from XV1000TR1

Sorry ,
my technical english is a bit poor, i´ll try anyway,
if you use the left side cover of the TR or 920 with chain drive, you also have to use the shift mechanism that works on the shift axle , on the left side. That thing with the springs, where the lever sits on outside.
In that case you can use the different sized shift axle, it fits better.
With the clutch , you don´t have to add 2 plates, you can use the plates of the BT, but you have to cut the things(no idea how they are called ) where the 6 screws and springs are located, in line to the outside of the inner hub. A normal metal-saw will do, or a lathe. Look at the TR / 920 hub, you will see what i mean.  
For using the right side cover of the Tr, you have to use the clutch plate ( that alloy Plate where the springs sit in) of the last mentioned. Measure the clearence to the inside of the cover, if there is not enough space, grind the plate down a bit.

I prefer  the clutch with one more friction-plate, this will work when you change the metal plates , the ones of the BT have 2.5 mm (or so, rememberance) , to TR parts which have 1mm less. Also change the last (inner )  plate to a one with the smaller /smallest thickness, which is secured by a wire. Then you will have enough space to put in one more friction plate. Put on one more spacing ring to the clutch plate bearing, and you will have a clutch that will not slip, and easy work at the handlebar lever,
I hope this makes sense, it is difficult for me to describe things , even more in english,
Ali

addicted to TR1

Cylinder heads BT1100, TR1, XV920r: all the same size of inlet and outlet valves

Camshaft lift: all the same cam lift

Timing: TR1 and XV920r same timing (longer than BT1100), BT1100 shorter timing