With "1978 Magnum" in the title, I'm sure Bill, the MagnumGuy, will be by with some input.

I know the plastic bits fail. But I don't know the interchange between 2 and 3 speeds.

I'll send Bill a text and see if he can tell you more.

DynoDave
Walter P. Chrysler Club - Great Lakes Region
Member # 12304
1970 Plymouth Duster
1972 Dodge Charger Rallye
https://wichargerguy.proboards.com/
1977 Chrysler Cordoba