The best way is to get a spot weld drill bit, it's intended for this type of work and makes it alot quicker and less destructive to the steel you want to preserve.

http://pengaru.com/~swivel/cars/rx-7...w_IMG_3161.JPG

Heres my car.
http://i9.photobucket.com/albums/a68...ini2/Inter.jpg

http://i9.photobucket.com/albums/a68...ni2/inter1.jpg

in that above pic has anyone cut the metal in front of the shock tower, meaning behind the passenger or driver door theres more metal there

If i remember correctly, it was a custom built cage from another car that my friend cut out and had it welded into this car before he sold it to me.

what about that cross brace n back of the seat