How do I tell if I have a 225

The block casting number is for a '68-74 225 engine...(198 used same block casting number)to be sure find the numbers stamped on the top surface of the block,same sealing surface of the head gasket, below the front spark plug, above of the coil/alternator bracket. You will usually have to scrape and clean away grease and it is faintly stamped. I always clean with a rag and brake cleaner.