First the before pic:

You can see the battery box was still attached. I wound up just cutting around the welded nuts to get it to come loose. The bolt head were gone from inside the box.
Here's what the patch panel looked like. I was going to just cut out sections and patch the original panel but the replacement is not exactly like the original. So I just decided to cut the area out and preserve as much of the critical edges and impossible to replicate curves as possible.

Battery box out. I will probably try to get a replacement, though I have not decided yet.

Pan with no box under it:

I checked the fit of the patch panel and drew a line to guide cutting. I began on the inside of the panel next to the tunnel:

Old metal gone. I have some prep work to do before the new bottom can go in. I have to replace the metal *around* it. Whew!

I took the new panel and trimmed it to fit along the outside vertical edge. I just could not wait to see what it will look like. Nothing welded, just a fit check and then back out:

Here's the inside edge of the patch. I will cut off the wide flange since I have enough good metal to stay away from the curves of the tunnel.

I'm going to begin patching around the new floor tommorrow (Hopefully) and will have more pics when I can.
For those of you who want it, here's the link to all the pics I took:
http://apollosaturn.smugmug.com/M37/Pas ... 3464_7iPWM