The 152 has the same sized cabin as the 150L&M. Earlier 150's are more narrow.
O-200's do stick valves, though I've had the same problem on my Lycoming 360. I think it's the luck of the draw with valve sticking. As long as the exhaust valve sticks open, it's more a nuisance than a damaging problem. Never good, but if the valve sticks open, a bend pushrod, or broken rocker boss is low risk. The pilot can greatly reduce the risk of stuck valves with careful engine temperature management.
The Lycoming 320/360 seem to have earned a better reputation than the O-300, though the O-300 has the same carb on oil pan arrangement, so the carb runs a little warmer. Carb ice is easily managed, and a carb air temperature gauge is a good idea.
Both types are having some structural inspections now a days but if you find well cared individual these shouldn't create big surprices.
The structural inspection is a burden, but the bigger issue is what is to be done if a defect is found during the inspection. Will the parts be available? Getting the wing bolts out of a Piper Cherokee series for the spar inspection, let alone getting the wings off, is a big task. But you have to have a plan, in case the inspection finds a crack. In the case of the Cherokee, a crack will scrap a wing spar part. The 172/182 has a repair kit which allows a crack in a specified area of the underfloor bulkhead to remain as found.
Your pre purchase homework is to hire a mechanic to do a pre purchase inspection, and as a part of that effort, have the mechanic research the availability of replacement parts you could need, if a defect were found in the future.