Revisiting...
I bought the return spring bracket a few years ago when I visited this issue last.
It looks like a very good match to the picture that Jeff shared. Thank you Bob for that suggestion.
Now I am looking at the hardware to attach the bracket. I found the 42758-S2 bolts as AMK B12311 for phosphate & oil and if the same bracket would be used on 390 or other BB, AMK B-13233 for Zinc.
I previously purchased from AMK a pair of bolts AMK# F-709 (for the AC brace that is attached to the rearward hole, as pictured in Jeff's photo). The AMK# F-709 has one of the AMK# B-12311 phosphate bolts included.
Today, I stumbled onto the pages in the Osborne 67 CHASSIS manual, (page 40 & 41), which cover the engine-mounted throttle return spring bracket(s) and associated hardware. The 2-pages cover manual trans & auto 67 Mustangs, all V-8 engines.
Dead center, top of page 41 is 289-4V AUTO TRANS, which is what I was looking to know. My questions for what I need have now been answered. CORRECT BOLTS for 289 4V-Auto Trans are also 42758-S8 (zinc, like the big block M.T. 390's use in the same location).
FWIW, Notice the return spring hardware differences on big block vs. small blocks AND the opposite usage of return spring brackets between all-4 combinations (both engines, M.T. option & Auto Trans option). A quick glance, you may miss my point.
My point? You may notice how on page 40, it shows 289's with a carb stud-mounted return spring bracket for M.T. cars while on page 41,the auto trans 4V's have the manifold mounted bracket...then look at how it is just the exact opposite on the 390's. STRANGE!
Jim, did I miss the spreadsheet having a line-listing for the 289's using 42758-S8 on the 4V-Auto Trans applications?