Is An Engine That Was Rebuilt 10 Years Ago And Left To Sit Still Good?

I sold mine for $150 and it was a good tight motor, used no oil, no smoke, nothing. I`d look around some more if I were you.

I sold mine for $200, with the original radiator...$400 is too much. Beyond that, if it runs, it runs. I would drop the pan and look for sludge or debris that may have gotten into it over the past 10 years. Replace the wires, belts, oil. Rebuild the carb to make sure it is working properly. I would definitely pour some sea foam in it and then change the oil.

A lot depends on how properly prepared the engine was before starting. After sitting for 10 years, the cylinders should have been filled with Marvel Mystery Oil, transmission fluid or such, purged and oil system primed before attempting to start it. If not or if you don't know how it was prepped, I would be leary at that price.
My $.02,
Gene

i agree that $400 is too much to pay. i can put my hands on a builder 200 for free, the guy doesnt do anything with 200s, only 250s.

I wouldn't trust a motor that has sat that long, unless it was properly stored (eg. new oil and filter, coolant drained from block, oil in cylinders and both intake and exhaust sealed from the elements. What would worry me the most is the chance of burning a valve(s) (whichever ones were open) from corrosion that formed over the years as well as rust and scale in water jackets.

I wouldn't pay $400 for it either, but if you're really keen on the motor you could go with some tools. Pull the plugs and shoot a little WD-40 down in there and then take a breaker bar and see if the engine turns over. If it turns it will probably run. If you can't easily turn it over don't even bother with it. Since it's been sitting so long I would say it's worth less than a high mileage engine that's at least run recently. Be prepared that if you buy it the seals might fail shortly after you put it into service. Seals tend to shrink and harden when an engine sits like that. I still think you should go with a 302, though. I ended up with a 302 in my '70 because I had it laying around. I tried to sell it for $200 and no one wanted it. So I swapped it for the 250 that was originally in there. Best thing I've done to the car. It has lots more power even with a worn out 302 in there.