I'll answer what I can although I'm not real familiar with M47 equipped models. First off, I'd take the dented rear shaft - the dent may not mean anything balance wise--and you'll know soon enough when it's all together. That way you know you have a rear section to fit the front - or something to match up in the event you do need a different rear section. I hope you marked them because the front and rear are balanced together. If the connection at the M47 is by normal U-joint there are only two solutions to the front section/rear section alignment--one will be balanced , the other not. If you have the rubber disc type joint then there are as many solutions as there are splines in the rear shaft extension. If you use your original AW70 rear shaft you will likely have to have the two sections balanced (driveshaft specialty shops).
For your questions
a. I do not know the specifics. Measure the diameter of the M47 driveshaft rear flange--and that of the differential flange on your car.
b. See the explanation in the first paragraph.
c. I'm not sure about the phrasing of this question. You have to remove the four bolts holding the torque converter to the flexplate so the TC comes out with the transmission. That exposes the 8 bolts holding the flexplate to the crankshaft. Stick shift flywheels do not use the steel spacer you'll find behind the auto flexplate.
d. It is possible to change over the firewall insert but that's a big job. Be careful to drill the hole the same size as in the M47 equipped car or the clutch cable will not be secure. All pre-1986 240's had provision for stick shift cable and stick shift hydraulic operated clutches with cover plates and rubber grommets.