Bigger Rear Shocks??

I recently put 15 inch American Racing Rims on my Mustang II...well after putting shackles on her to raise the butt a little, she still rubs a tiny bit on those rolling sharp turns...if I raise her one more slot higher, the shock will be fully extended...I already uses shock extenders....Was wondering if anyone knew of a bigger shock that will fot on the back of a mustang II that will take care of this....I'm not a huge fan of air shocks, but only as a last resort....Thanks all!!
[addsig]