Casting numbers are not necessarily part numbers. The June 1957 revision of the GMC master parts book lists a p/n 2193486 to fit all of the 228-302 series blocks. The January 1962 revision shows a 2326722 to fit 270 and 302 like Tim posted. They will all interchange, but you need a distributor designed for cast on the cast iron cam and a distributor designed for steel on the steel cam. There is probably no noticeable difference. If you are looking for performance, you need to look at an aftermarket cam designed for performance.