Slant Six Identification Help?!?!?!

hey yall,
I have a 1960 plymouth valiant v200. i've had a time trying to get parts for this car. for one, the wheel bearing went out, finally a parts store guy used digital calipers and a book and just "matched" the size to something to find something that would work, ended up being a sealed bearing which is what i had and apparently started in 1963, so ok someone changed the rear end sometime or another, not too big of a deal since i got it fixed now...

now my water pump is starting to rattle and i need to replace it. the parts store want to know which motor i have. i have checked the hose between water pump and head and its short and like 1" to 2" so 170? but the parts store says the computer says in 1960 there were no 170 engines only 225's. i cant find any numbers where everyone says to look. the only numbers are on the drivers side of the block.

does anyone have a way that i can check to see what size slant six i have?