Firstly you can't compression test a 2 stroke the same way as a 4 stroke as the case seal is as if not more important than the piston seal, which is marginal at best on a 2 stroke.
Your basically tossing a coin here, 2000miles in 40years could be a death sentance or it could be ok, mainly its down to the seals. They age and can perish and that i would say is your biggest worry. The pot and the piston are unlikely to have issues bar maybe gummed rings so long as the bore hasn't rusted.
The gearbox internals may also be fine, but again could be part fine and part rusty mess due to the oil not moving for 40 years.
Basically if you live on the cost and it was last run in 1978 it may well be shot, but if your in texas and it has been used 4-5 times a year to blow the dust off it could be good to go.
Can't say more really....... apart from replacing all the seals and bearings, available readily enough here in the uk for under £100 (cheaper if you chance the crappy pattern stuff) so its hardly a disaster if the seals have gone.