10j is probably 5 bearing metric not the 3 bearing imperial original. Gaydon supply manufacturing records given a vin. If it's military then that has an accessible history as well. If it was petrol then it just means someone put a later diesel in. Do you have all the old mots? Don't think...

Broken shaft at the front? Can you jack up the front then turn the wheels to see if the prop and other wheel turns? If that seems ok then I'd assume it's something in the output box. Maybe take off the front cover and check the selector shafts move ok.

Is the pump definitely going round? You won't get a squirt at each port for one rotation, it will only be one port.

Think that would be terminal on manŷ engines rather than just running a bit lumpy.

Yes please, let's do twin speed. Then intermittent. (Can't be too hard - can it?)

Grinding changing down from 4 to 3 could be just the synchro. Try hesitating before putting it into third. It's quite easy to beat the synchro on old gearboxes by trying to rush them.

If it's taken 5 litres then you're wasting your time repeating the same technique. Try back flushing or pressure bleeding. And isolating the problem by clamping the flexis as mentioned above.

Whitehouse & sons, Aztec engineering or beaumont are known to be good. Synchro gearboxes are interesting but I don't know anyone who's used them. Or take pot luck on eBay

Could be the master but if you're losing all the fluid, you should easily be able to see it. If the cylinder bore was dirty or corroded then excessive pedal travel will put the piston on a rough bit of the bore and wreck the seals. But if it's leaking, it's knackered anyway.

It's "worth" what someone will pay for it. And you can't buy them new, so why not?

If the pump was jammed (not sure how that would occur) it wouldn't run at all. If the linkage is on the tick over screw, the other thing that would make it rev is sucking in oil. I'd check the compression and turn it over with the glows out to see if anything comes out.

As above particularly if the temp gauge is still working. Also, if you earth the sender wire, the fuel gauge should go full scale thus proving it's the sender not the gauge.

Wear platform shoes.

Stand on a box.

I fell off my bike and broke my wrist. The doctor said that particular break used to be called a chauffeur's fracture because they used to be common amongst those using starting handles. Hope that helps.