If you backed the self adjusters out as much as possible before you couldn't get the drum on , that's all you can do. Did you get and install all those missing parts especially the bar because that is what applies the parking brake. If so, then all you need to do is check the parking brake cable that runs along the driver's side of the chassis. If you have the back wheels up off the ground and apply the parking brake the wheels should be locked. If not, pull on that parking brake cable and see if that locks the wheels. If it does, just shorten the cable adjustment. The procedure usually says to tighten the cable so the wheels lock after 3-4 clicks of the parking brake application. It's not that critical as long as they don't drag or as long as the application holds the vehicle parked. You need to be particular since your being able to stop the vehicle is shall we say quite important. I would like to know if you solved your problem.