Here you go Andrew, half way down the page...
http://home.flash.net/~sanco/mustang.htm

This area (I call it the "suspension cup") is commonly rusted out from mud sitting in there so it can definitly use some reinforcment. I dont have a welder or I would have done it myself..
Nic

 

that definitely looks like a good thing to do. Wonder if that is applicable to a 65-66?

 

I havent seen the area behind the suspension on a earlier Stang, probably though. Maybe a different shape..

 

Why not run a full frame like http://gmachinechassis.com/

 

that might be a little expensive. although it would be the best thing.