After reading some of the replies, it made me think I may have misread (and misinterpreted) what was on the Shelby American invoice to Dale Wood (and remembering that occasionally folks have referred to the override and underride traction bars as stabilizer bars), I went back and dug into my books again.
I found the part numbers for the override traction bar kit (S1MS-18127-A for the complete kit) and S2MS-18127-A and S2MS-18128-A for right and left side underrides (respectively), so this (along with the fact that the base part number for a front sway bar being '5482' indicated (to me anyhow) that the part number I have on the invoice to Dale Wood is indeed for a rear sway bar. Unfortunately, from the 1966 and 1967 Group II Mustang Bills of Material don't show a rear sway (stabilizer) bar in the listings (of course, they could also just be the material lists to build a base version of the Group II cars for those years). However, in the course of digging through my books, I found that the bar is supposed to be 1/2" in diameter (Rick Kopec's article in The Shelby American #44 and the 2011 Registry both mention a 1/2" bar was available as an option for the Group II cars). I also found a copy of Shelby American Race Assistance Technical Service Bulletin #1 (dated October 10, 1966) which gives a verbal description of the S1MK-5483-A Rear Stabilizer Bar Kit (described as being permitted on Group II cars under FIA rules). These and the aforementioned invoice with the part number are all I have to go on so far- but not a single photograph,
Interestingly, Earl's photos and Dave's description of the DOZX bar made me remember I have a nearly identical bar, except for being 1/2", out on my barn. This bar even has the same tab with three holes and the same type end links (Heim jointed on the top and rubber bushings on the bottom). If I can't find the specs or photos of the S1MK bar, I may end up going with it instead.
Thanks,
Dave