I say that but many of the people still insist on putting the information into the computer. When I was looking for a serpentine style belt for my 66 the guy told me they only had the single rib and even brought some out to show me.
They'd definitely have a hard time with mine. I've got a two-belt March system with a Chevy PS pump* and a Sanden style AC compressor.
*(Incredibly, the factory (replica) hoses for my power steering fit the pump, and the pump lives fine with Type F fluid.)