74 Duster Clutch Petal Doesn't Come Back Up

I have a 318 with a 3 speed. I don't know if that matters but I forgot to add that in my original post. Probably a dumb question but how do I know if I put a diaphragm style clutch plate in there? I bought the car from a guy who tore it all down and lost interest so it has been like a jigsaw puzzle with no picture so far.