To the best of my knowledge, Kenny Brown Super Subs are your only option. You may want to try and contact SpinTech about their subframes. I do not know if they are full or not.
FWIW, I took the KB SuperSubs off my GT to put on Steeda full legnths(with torque box plates too), and then put my KB Super Subs on my girlfriends 99 auto/V6/Convertable.
I noticed no difference at all in my GT, but the KB's made an ENORMOUS difference in her little 'Vert!
If it wasn't for her car needing........SOMETHING.......I would've left the KB's on my car. Don't under estimate the KB's, they really did good in my opinion. My GT also has a 4-point roll bar, and after I put those KB's on the first time, they still made a sizeable difference even with the cage already installed/bolted/welded down.
Good product!