BradH - I've weighed practically everything on my Challenger (originally a 72 318 Rally... converted to a detailed 70 T/A.. for SCCA Solo II autocross competition, ultimately for class E/SP). I've weighed the stock Challenger e-body seats at 45-50 pounds, (50 includes the factory brackets). I've replaced them with a light-weight Corbue GT8 seat.. very comfortable and great lateral support.. weighs ~18 pounds w/o brackets.
I've also replaced the passenger seat with a fixed light weight padded covered drag seat... weighed ~10 pounds.
Many years later, I've replaced both front buckets with high-side bolster reclinable fabric covered seats ... Garage Pro brand (?)... from JC Whitney.... each weighing ~28 pounds w/o brackets... allows easy access to rear seat area. I was able to first sit in these seats at JC Whitney (during an Open House with outside car show)... and the fit and quality was surprisingly very good, especially the high side bolster and low weight. and the price was very reasonable.
You should consider high side bolster -- hip area and lower rib cage area... many seats just don't have the high-enough support that is desired... shop around and actually sit in them.. some are a standard width some are wider ... pending your personal size.
Also, you can decide IF you want seat belt passage ways or not.
As I said in a previous memo, I suggest using the factory floor braces.. and simply add a couple steel plates (~1/8"-1/4" max thickness)... x ~2" wide, to be drilled and mated to the factory floor braces.
