Patched the floor back to "automatic", but as you can see its still going to end up being slightly wider at the front.
Fitting and holding the tunnel down with self drilling #10 screws
Current progress for the day. I would basically cut a section out right on the edge of the new panel with a cut-off wheel, install some butt-welding clamps, get the welding started, remove the clamps, hammering for fit as I go, and then switch back. It takes a long time, especially with the front of the tunnel since it's under the dash. That's also a lot of metal to fill in the middle so it burns away a bit sometimes. Overall, the tunnel is about as wide as the headers are at the collectors, so should be enough room to get a hand in there for at least most of the bolts without tilting the engine.