weight of parts
A/C is going to weigh more. Sorry never had one so I can not say how much more.
Back seat is around 20-25LB
Not sure on the fuel cell. But I know gas is around 6LB a Gal. So a stock 15 Gal tank VS a 10 Gal tank will shave 30LB in fuel.
The rims should shave around 40LB for all 4 of them.