If looking at an aircraft to buy, SMOH etc can be meaningless. Check in the log book what happened at the major overhaul. Understand Factory New Tolerances and Permitted Tolerances. Get YOUR engineer to look at the aircraft. The cheap way is to look at aircraft and logbooks yourself first, then pay your engineer to go and examine what you think is O.K.
If you can find problems, take your engineer's advice as to whether it's worth getting him to look at it.
And why did a LyCon with 300 hours need a top head overhaul??