I had a difficult time with the "replacement" ones I got from a supplier. They spun once installed. I ended up using some nutsert type that grabbed the sheetmetal better. I also put a small dab of loctite red on them before I installed them.

1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)