Back in the 70's and 80's you would look for these centers in the junk yards or swap meets. They were a low cost way to get the gears and sure grip if you were on a budget. And guess what they would live in cars with 500 hp and street tires most of the time. But you didn't tell your buddies that it was a 741 case but you now had good gears. So a bunch of them were swapped into to cars.