David, either way you go, with a whole pan, or two halves or smaller patch panels etc... all you would need to do (say in the case of the whole floor pan) is to measure, mark and cut the pan to fit up to where you need it, so say you need all of it up to just below the rear seat etc... then you just cut that section off of the new pan and your good to go.
Sounds like this may be the way you'll need to go? If you need part of the tunnel etc? I haven't looked at what is available, and you should know by now what's out there, and maybe you can just buy say the two rear sections, the tunnel and then the two front sections and just patch what you need?