@GearheadsQCE will know. I see they are 12 bolt, and as far as I know Halibrand is the only one with 12, all the others were 11, along with the majority of the Halibrand championship units.
Marty, your confidence in my knowledge far outweighs my memory's capabilities I have seen some plates like those before. They have some similarity to Nance live axle pieces. Pretty sure the are not CAE as the pic might indicate. @craigibc probably knows more about CAE than most anybody. BTW 12 bolt Champ QCs were made by CAE, ARC and Benson as well as Halibrand. I don't think Frankland ever made 12 bolt center sections but they did offer 12 bolt side bells. But, everything I've ever seen from Frankland has some sort of ribs or fins. I have some one piece 12 bolt axle tubes that look similar on the inside. Unfortunately, I haven't been able to identify the manufacturer of these either.
Now those are unique. What so you think they were used on? Looks like there's a place to bolt them solid to the frame.
Dave, I think the pads are for truck arms. A rear built with these would be pretty wide. Probably fit a late model.