nice find....

Id recommend rebuilding it straight away.... the chances are the the grease on the diff has gone bad, same deal with the ballbearings and the engine.

if the engine is full up of old oil that's turned into sludge or hard deposits its really worth flushing the engine out with WD40 before trying to start it, that will clear out the oil oil and help dissolve any rust.

same deal with the diff and wheel/gearbox bearings

my only other thought.... its a vintage engine and might be problematic. if this is your first experience with nitro engine id highly recommend getting help with the first run.
that way they can try to tune it for you and make sure there are no major problems....