Not much you can do to easily lighten up these cars beyond simple bolt-on stuff. Lighter wheels, lighter battery, lighter aftermarket exhaust combined might drop 100-120 lbs or so. Beyond that, yeah the stock seats are heavy, so you could spend big $$ and find a set of the optional carbon "racing" seats, or install aftermarket racing seats (Sparco/Cobra/Corbeau, etc), so maybe another 80 lbs or so there. Beyond that, you're looking at removing sound deadening material, maybe swapping the heavy stock aluminum hood for a carbon hood (more big $$, if you can find one) and then really tearing into to car to lighten it up more. Realistically, dropping around 200 lbs or so is probably about all you can do without going down a rabbit hole that would ruin the car's civilized GT character and require significant mods. Not to mention big $$$! Or, save your pennies and wait for a Prodrive 550 GT1 race car to come up for sale.