So you're standing at the parts counter.....

As a former "parts counterman" (some 15 years at two stores) just use the age old "They're all the same"

I got into one HELL of a mess with a drunk *** over a 350 vs 400 Chev, whatever he wanted it made a difference. "How do you tell?" I said look at the VIN you can not tell by just looking at the engine. "Bullshit there's no way you could get a 400 out of that little engine"

Yeh, well OK fine
My favorite is the lady who came in, said she needed to buy spark plugs for her car. "What kind of car?" I ask.
"Blue" she says. I knew it was going to be a long day.