Single groove means V-belt.
I can tell you the alt pulley I took off was tiny. (have it next to me)
Around 2 13/16" (~71mm)
I know ford makes a larger one than that for other 6-ribs. (IIRC they make 3 sizes with mine being the smallest - early Duratecs (95-97) had a slightly larger sized one for certain - never really looked for the switch date - probably 99 or 00)
I haven't really looked into it since I put mine on. I basically lucked into the piece and was happy at that point...
