Q1- I hope you have a workshop manual...
Much easier to watch someone do it, but I'll try.
You pull the diff out, then remove the spring, ball and sleeve from the RH side of the diff.
Then, with the gearbox in neutral, you rotate the selector shaft & selector anti-clockwise so it clears the bellcranks.
Then you use a big screwdriver to push 1st gear into mesh, and then do 4th gear also. This locks the shaft from turning.
You then need to hold the box from turning somehow, knock back the pinion gear locktab, and undo the pinion nut with a deep 1-1/2" or 38mm socket. It's only 150 ft/lb, unless gorilla joe did it up with a rattle gun.
Q2-
I undo the big clip and then knock the shaft, bearing & gear out with the mainshaft. It is not a real tight fit.
Q3-
After you have knocked the mainshaft in to remove the 1st motion shaft, You then put a split tube spacer on the mainshaft, between 1st gear and the mainshaft bearing. Knock the mainshaft back to remove the bearing. You can then tilt and lift the mainshaft & gears out.
Caution when pushing the mainshaft to and for as above, watch the selector forks don't get caught on the bellcranks or you will lose the balls out of the synchro hubs.
Disclaimer-
I am assuming you know what these bits are, if not I suggest you get some help.
The gears and their dogs do look very good...
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
