All 230 SL's had 230 engines, and all 250's had 250 engines. So the engine is your car is indeed not stock (original). If you order the data card (see elsewhere on this forum) then you can see what engine number your car had originally. The 250 engine is a bit larger in displacement, and has more main bearings. Additionally, prices for parts, should you ever need them, tend to be lower than for 230 engines. If the car runs well, I would leave it alone; there are many Pagodas that have non-original engines; the 280 sedan injection engine is a popular replacement for non-repairable original engines.