How to stiffen the body without adding a rollbar ?

[DOUG H]

SCP still carries Torsional load brace for rear, Front suspension subframe brace & engine cradle stiffiner's
as 95 XR7 noted in 2010 ( in post above yours). Click on SCP in his & it'll take you to there site.

 

[Mercutio]

Seam welding would probably help.

 

[racecougar]

SFC's did end up making a big improvement. Installed these around 2011-2012.