In Need Of Some Guidance... ('67 Coupe Floors)

Hi guys,
I just acquired a '67 coupe that I'm about to start restoring. The body is great, but the floors and rails are not... My buddy's dad is great at welding and I'm not too worried about us boxing in the frame rails. But the floors have me worried. I'm kind of stuck between buying a full 1-piece floor pan, or buying a pan kit on cjponyparts. Besides the actual pans, another part what I believe is the floor support (the part that you can see under the car, beneath where your feet would be) is completely shot and is filled in with expanding foam. I figure I might as well save a little work and gain a little more strength and get a 1 piece pan. I also think it would be beneficial to have the floors out while boxing the frame in too.
I guess my question is how to go about doing both these jobs. I know if I take the whole pan out I will have to support the body somehow so it won't bow, but can I replace the floor support while the floors are out? I've also been hearing that I can fit the 1-piece floor through the door window of a coupe and won't have to take any windshields out. Just wondering if that is correct also? I would really appreciate some info back. Thanks.
-Tom

I've been talking to a guy from the cjpony parts shop. They seem to be wanting me to just buy the pan kit (do each side separately) and leave the trans tunnel in for support since it's in decent shape. They also want me to replace the drivers torque box and add one to the passenger side. I will definitely check out their build threads. The problem is that I can't see everything because the guy before my put floor patching on the entire underneath of the car... I really appreciate the info, I'll try and get some pictures up so everyone can see what I'm dealing with.

I'm nervous about removing the whole floor and the car bowing. If i were to do this, what ways could i insure that any bowing or twisting won't happen?

Forgot to mention also that the engine and tranny are out of the car. I guess that would be a big factor about the car being under less stress when doing this job.