I've owned and race several different 1963 Plymouth M.W. Belveder, a sedan and a hardtop. The sedan needed to weigh 3320 without the driver back when NHRA weighed them according to the shipping weight, the hardtop needed to weigh a little more.
I converter the hardtop into a bracket car with a Alston 12 point cage, subframe connectors, full size steel wheel tubs to the stock subframes, moved the leaf springs into the sub frames and ended up using a Dana 70 with a posi unit in it and 5.13 gears,
That car weighed a little over 3550 lbs. without the driver with a single fibreglas seat with a small thin wall tubelar frame, no heater, radio, windshield wipers. It did have the stock door panels and full carpet inside up and over the rear package tray