interesting ,, my 71 has 72 doors from factory

[58 Special]

I converted my 71 GMC K15 suburban to 72 door panels over 25 years ago.
Finding a good set of regulators for the front was fairly easy then, as they are the same as all pickups. Finding rear window regulators for the back windows was another story. After looking for some time, I finally took my original rear regulators drilled out rivets and replaced with longer 72 posts. about 6 months later I stripped a 72 suburban with proper long posts. Those regulators are still on the shelf.