Pete. If the crank has been reclaimed at some stage by fitting a sleeve and grinding to size, I would expect the sleeve to extend the full width of the timing bush (yours looks shorter) and have a groove and oilway to supply the big ends. This looks to be absent. Just wondering if this is a temporary codge by the vendor give the impression the engine was OK internally when you went to collect it, and it was never intended to run.
As far as I know, 40 thou U/S shells are the smallest regrind size. So unless you are absolutely sure it is basically a sound crank, another crank is your best option.
Sod's Law says now you want one, there are non to be had. So, pretend you can't be bothered. One will appear. Instead do something simple, such as wheel bearings or brakes.
I would save checking the gearbox until you have achieved a little success.....It will probably be just as bad as the motor, and there is a limit to how much more stress and anguish you need.
Keep posting your progress, best of luck, spanner on.
Swarfy