You can check out this link to find both upgraded hard parts, shift kits and technical info on setting up and improving the 4L60. With 50k miles on it, it might be prudent to freshen the entire transmission if you are going to be in there.

https://www.sonnax.com/gm_4l60e

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)