how to identify a slant six?

It's straight down from the number 1 spark plug right where the valve cover meets the block behind the alternator bracket. It might be a little grimy and hard to see if it was like mine. Mine said xx 198 so it's a 198 slant. If it has the original engine yours being a 72 would only be a 198 or 225. They didn't make the 170 after 1970. :)