subframe stiffner

Here's an exelent set by xv motorsports made specifically for a bodies:
http://www.xvmotorsports.com/products/detail/index.cfm?nPID=16&cid=40&cdesc=A-Body Products



uscartool has a set like that too.
http://www.uscartool.com/Aframeconn/index.html



Or you can make a set your self like I did for under 20 bucks.