Alternator Pulley Question

[horse with no name]

Hello fellow Mustangers!!

Just a quick question... I am looking to purchase a PA 130 Amp alternator for my 88 GT. On PA's website they give you options as to what Pulley to get with your kit. This is kind of a stupid question, but which Pulley is the correct one? I am guessing it is between the 5 and 6 Groove? I counted the number of ribs and there are 5, however i was not sure if you count the outermost as Grooves or not... The options that PA lists for Pulleys include:1V, 2V, 4S, 5S, 6S, 7S, & 8S.

Any advice would be greatly appreciated!

Thanks!

'88 GT
World Class T-5Z tranny, Hurst Short Throw Shifter, King Cobra Clutch Kit, Mac H-Pipe, Mac after Cat Exhaust, Fluidyne Radiator, Optima Red Top Battery, Maximum Motorsports Brake Upgrade Kit, Power Slot rotors, Edelbrock Timing Chain. Many more Mods to come...