Was it stored outdoors? Stuck rings are possible as mentioned. If you have a blown head gasket(rare in these engines unless it was overheated) you may see bubbles in the radiator or hear hissing with the leakdown test. Can you use starting fluid and get it to run(at least to determine if there is internal damage and oil pressure) before you expend a lot of effort. With no history it could have been parked for many reasons. Also regarding the heads-most any engine will need the heads rebuilt. These are notorious for worn valve guides.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT