engine top overhaul

(IO-360-C1C, 2000 TBO) My engine is running towards 1400 SMOH (/500 STOH). I started to wonder if one is required to an overhaul or not for the legality. My insurance states that the airplane needs to be an in airworthy condition. I checked the FAA documentation and that is rather vague as to...

Hello. Looking at an airplane that looks like it's been a sitter for a long time. IO-360... pulls through, has oil in it. Oil smells like oil, nuthing funky. Has about 1400 hrs. SFOH Anybody know the cost to do a top overhaul on an engine like this? I'm trying to build a budget... I'm betting...