Can a marlin model 55 36in goose gun shoot a slug?

Slugs in Goose gun? Not a good idea to shoot Foster slugs in full choke, although it can be done safely, accuracy will suffer. That's Foster slugs only! Remington and Winchester.

It's better to have a screw-in choke system installed, then you can use an open choke tube for slugs. Try Johnny's chokes:

www.angelfire.com/ok2/shotgunchokes/index.html