Just wanted to share what I did for radiator coolant reservoir. I bought a 1975-79 nova bottle and mounted it in the passenger fender behind the battery. I did have to drill a mounting hole in the fender and had to pay attention where to mount it so the bottom of the bottle wouldn’t rub on the wires that come through the inner fender. The bottle does have a recessed channel on the bottom so that works out nice for those wires to run through.