FYI if you decide to use the later 68-70 style then I have a bracket just like in Jeff's pic that I would be happy to give you if you pick up the shipping. it would a indexed pulley/shaft pressed in (taken from a more common upper SB/BB adjustable Mustang one) .
Bob, thank you for the offer, however, since this 68 was built in Nov 67, I think I'd prefer to look for the 67/early 68 version. This will mean locating the A/C bracket and both the upper/lower idler pulleys. It'll cost some extra but I think I'll be much happier when it's complete knowing it's as close to factory original as I can get.
Also, the picture with the complete set up will be very helpful when searching for the correct parts.
Thanks to all who contributed (Jeff!), you guys do a great job helping us all to be true to the passion of Mustang restoration, especially for us armatures. Keep up the great work.
Lee