If you want to go 16", get a pair of used 3rd gen RX7 stock rims (16/8"). Not sure what the offset is, but they fit the back of the TT Supra like a glove, and you can mount 26 x 11.5 x 16" ET Street on them (or 26 x 10.5 x 16" if you want to be legal for sanctioned events, in Power 6). I picked up a pair of those rims for $170 shipped. Hope this helps.
Forgot to mention, they are super lightweight, 15 Lbs or so each.