I just hit personal paydirt!!
My almost OCD level of three speed parts scrounging has paid off!
I just confirmed via a master parts manual, spurred by discussion on NastyZ28 that the reverse lock out rod used on Saginaw 3 & 4 speed cars, is the exact same rod used on Muncie three speed cars!
Group 4.035 "ROD, STEERING COLUMN LOCK" (lower, not upper rod).
I know this is specific to Firebirds, but I figure it's worth mentioning here incase someone in the future can use this information.
I bought an ITM 3 speed shifter & reverse lock out rod some time ago from a membber here, and filed the parts away;
It appears as though unlike the Muncie reverse rods which had stamped (abbreviated) part numbers, the saginaw rods do NOT have a part number.
I'm attaching an image of a members former(?) car with the rod shown so that the shape is clearly seen.
This is NOT the rod used for Muncie four speed, or Borg Warner four speed cars (both of which ARE different).
Also, you need to confirm that you have the correct bell crank, and reverse lever on the transmission.