[Mart]

Have a look where the spring attaches to the axle. If the attachment points on the axle are part of the axle casing, it is a 37-40 axle. If the attachment points are on an extension of the radius arms and are bolted to the axle then that is 35/36.

In theory any complete rear end assembly 35-40 ought to bolt in. Obviously if it is exacly the same it may be simpler with regards to running the brake lines etc.

I meant to reply earlier to say that if you jack up the rear and pull each wheel, one of them ought to pull right out. This will confirm the broken axle diagnosis. If one does not pull right out, it may be because it is catching on the brakes or safety hubs or retainers have been fitted in the past.
One other thing, is the speedo working when the car is supposed to be, but not driving? If it is it means the problem is rearward of the gearbox, if it isn't, the fault is in the gearbox or clutch.

No harm in doing a little testing to try and isolate the problem.

If it were me and the tests show it is an axle, I would first get an axle and then only partially dismantle the left side of the casing. This would allow the diff unit and the axle shafts as an assembly to be withdrawn. they can be fitted up with new shafts and reassembled. With luck, if the gaskets do not get torn it can be bolted back together and back up and running in a relatively short time.

Mart.