YES 5.9 Magnum manifolds work in early A bodies. Here is exactly how!

Surprisingly the pin popped right out
Thats great, I beat on one with a hammer once and it didnt budge. ended up cutting it off (manual length) and grinding it to fit a deep 5/8 socket and using a 3/4 drive U-joint in some sort of death trap socket to socket weld up derby quality mess. It worked but I wouldn't drive my mom in it.