Very clean car! As far as weight, I know in stock my car has always been very close to weight (i run alum arm supports and IRS rear bulkheads) so in mod i normally run the stock rear bulkheads to get dead on with weight (since mod motors weigh a bit more), and I normally dont run an rx pack which normally weighs around an ounce.
If you want to add weight one of the better places to do it is to drill a hole through the lead weight and then use the two holes for the battery brace in the back (since i almost solely run the batts in the back position, since the car steers so much already) and then just basically bolt down the lead weights (you need to trim them so they dont hit the rear pod), but justin johnson (aka bevis) i saw had run his weight like that for cleveland.