brakes not working right

I didn't know they made vehicles in 1973ish.
I call it that after finding out the engine is 76 or newer, the rear end is probably '72, the drivers side door is not the same as the passenger side, so I have no idea what year it is. Which is a problem as it's missing the part that keeps the window from flopping around, which is clearly different than the one on the other side.
It's a frankenstein '73ish car