Fan belt on 68 C-20 no accessories

[Happy_dan]

Another of those really simple questions for things I should probably know.

I have a 68 C-20 with not accessories. Just the fan and alternator.

I replaced the belt and it seems to fit in the pulley quite well, but if I am sitting still and push the throttle by hand quickly, I get a squeal.

It's not the water pump since I out in a brand new one when I rebuilt the engine.

Does anyone have the part number for the right belt just so I am sure I have the right belt?

I believe what I have on there is a 15530.