Took a while but I came up with an idler pulley. It's a Nuline EP127 (60mm), actually made by Dayco but a product of Australia and go figure Magnacharger used to use them and had a few left on the shelf. I found a 114.5 Gates fits tight and now I'm just waiting on my tuner. Unfortunately he's down a tech and backed up a few weeks but I've got plenty of belt wrap now!

 

looks good

 

Update. Finally got in for a retune a few weeks ago and have been DDing the truck since. Mustang dyno pulls in second gear were good for 450hp on the nose. It looks like adding the overdrive pulley and meth was only good for an additional 15hp on this set up. Kind of a bummer but oh well, this is all leading to a larger head unit in the future probably a whipple 2.9 because my little 112 is beyond out of breath. Dyno sheet below. Sorry I don't know how to rotate the image.

 

Well Ill bet it runs pretty strong at 450.