Because of the hundreds of options available at the buyers request at the time, I dare say there are no figures available for any particular vehicle off the assembly line other than the very bare production model. For example, my factory GT 66 coupe was supplied with delux options but no A/C, no pwr steer, no centre console' no LSD, no luggage rack, no compass, no brake warning light, no remote control boot release, and as the sales brochure (which I have) says "PLUS MANY, MANY MORE-OVER 70 MUSTANG OPTIONS IN ALL". And, my GT could have been a dealer optioned GT which would have been slightly lighter due to structural additives during manufacture. Weigh bridge is the obvious solution, but how do you convince those turkeys.
Good luck!