thinkness: most guys use 1/8 inch. that is .125'' that is what i used too. pictures are a few threads down in the torque box reinforcement thread.
suggestions: measure twice haha. it is a real bitch to get everything to fit nicely. i everything with a sawzaw, take your time and measure twice and you can get some decent cuts. make sure your frame is level... drop plumb bobs to the floor and measure from three different reference points. drop a bob to the floor using the same refernce points in the front and back to make an x pattern when u measure. when you cut the floor make sure you cut it to narrow if anything it is a huge bitch going back in after to weld the floors to the frame if you have a huge gap.
are you gunna put a cage in? i strongly suggest running an out rigger to the rocker box to mount a cage to. and anywere you have a the new frame butting up to the car ( rocker box outrigger / rear bulkhead wear you meet the rear subframe) weld a plate of 1/8 steel inbetween the frame and the stock thin sheet metal. it will be alot more rigid and give you alot more to weld into. good luck and have fun with it! if you need any help let me know and i can get you more pictures of what i did.
