I had to recently replace a couple of cracked cylinders on an O-320-E1A.
Too the opportunity to upgrade to a higher-compression 320-D1A by getting higher compression cylinder kits, which gives an extra 10HP.
Check the specifications of other similar 235 engines to see if they came fitted with higher compression pistons.
Probably not worth it if the engine is ok, but if you need to replace the cylinders/pistons it will cost about the same for the higher compression parts. You might need an Engineering Order.
Lycoming sells kits that include a cylinder, piston, rings, gudgeon pin etc for about $1,200 each.