Stiffen up my topless ride?

I just recently purchased and 87 turbo supra......i have had a few nice days lately and have decided to take the targa top off and go for a few cruises. I can't help but notice that with the top off the car kinda rides like ass. Obviously there is a lack of support now that the top is off but I was wondering what i could do to possibly give myself a lil more stable and stiffer ride so i don't feel like my car is gonna twist in half or something. Does anybody make like sub-frame connectors? or if i put some new suspension in the car would that help? If anybody has any suggestions please let me know.

Yes a stiffer suspension would help the car...and sumthin as simple as a sway bar could help