no "necessarily" about it Sam, our old low compression 235's do fine without hardened seats, tho most [not all] will go that route if the engine is being rebuilt .... valve seat recession has to do with adjusting the valves too tight, way more than the type of gas, and if the 235 valve train doesn't have a nice 'sewing machine sound' they're too tight and you'll have problems regardless of what seats are in it ... go with the designers specs
Bill
