A buddy of mine has what looks like the tan ones, in his '70 Dart.
The reels are pretty huge, and running that extension bracket, the reel pivots around and isn't secure to the rocker like a normal OEM deal.
As a "bonus" the damn thing can abrade the door trim panel.
Relocating the anchor point would help his installation out, but so far he's against doing that.

I can't help but think that a later A OEM setup would be much better, but they apparently aren't easily found in good condition.
Maybe the factory relocated the rocker attachment point for the later cars ?
A-bodies are a lot tighter than B-bodies in that area.