Bringing this back up from the dead for future reference:
Pulley: Gates or AC Delco part #38002 is the 100mm pulley that PPE uses, it has a 17mm ID bearing
ATI Products spacer part number 915993 will space it .35" and bush it down for the 10mm bolt like the PPE spacer
Or you can use Gates part # 91051-15 bushing to bush it to 10mm and a spacer to get the correct offset.
Or you can use an LML shouldered bolt part #11515769 so no bushing is required, but you would still need a spacer to correct offset.
I need 2 of these setups for the belt driven air compressor setup on my LMM and am going to use the ATI spacer and the LML bolt so the bearing is basically bushed on both ends. To play with belt tension you can find larger and smaller diameter idler pulleys on the Gates site and most are 17mm ID bearing. Gates 36299 is 90mm OD and comes with a spacer and bolt that I think will bolt right up and work.