Speaking of changes from 60s/70s.
In photos from that era you see players with a ton of pads on their arms/hands.
Few pad-up like that anymore and people assume its to be lighter and faster.
The real reason was line players and LBs couldn't use their hands - they had to use forearm "flippers."
The flippers were using arms as impact levers.
If you were a DL you threw your arm back at snap and then swung it in and up to a blockers chest.
If you were a pulling guard you hit your target with your forearms arms folded like a battering ram device.
Once players could uses their hands the flippers and battering-forearm blocks faded off and players didn't need all the pads. Arms and hands could get pretty sore throwing them around like clubs on guys dressed in plastic shells and helmets.
Sometimes I wonder if the old blocking style (when DL couldn't use hands) helped OL block better