i dont think there is any issues with using the old classic models, of course segments assets wont work, and most of the characters will need seriously looking at for different issues but all packs on sale should be fine.
i have a couple of packs myself + the one's that came with gold pledge, some work without converting or did last time i tried them, (this was before lua though) and tgc are in the process of updating 400 models from the gold pledge selection of packs, (though i doubt if any are characters tbh due to the issues there are with some if not most of them).
evga GeForce gtx 750 ti boost2.0 2gb gddr5. win 8.1 quad core 4gb ram.