Plaza sedan is bottom line 58 (or near it) and I'll bet it's lighter than some 70s A-bodies. Aluminum head 408, and a 904, would be a couple hundred pounds less than an all-iron poly, and iron powerflite.
Edit: Plaza is even down-scale of a savoy in 58. Two door sedan probably the lightest 58 Plymouth you could buy. Frankly, I'm surprised it has a poly and auto, I would have expected a six cylinder flattie and a three on the tree.
