Pull the plugs, crank a few turns (just in case), plugs back in, start, listen. If it had hydrolocked in the past, and bent a connecting rod, you'll know it.
Its not always evident by listening.
You need to measure piston heights in pairs (1-4 and 2-3) and compare. Only way to know for sure.
I bought a parts bike that wouldn't allow a full 360 degree engine rotation as the bent rod would make contact and prevent further movement. It was only 270 degree total until lock. I suspect multiple hydrolock events occured to hammer this into such bad shape. No way to know if the owner could hear anything as a tip off when the engine was running as this condition progressed. No doubt there were start attempts that ended with an abrupt clunk.