Hi all, I just used the outer sill trim section,the bit that's bolted on under the door- it's u section angle and well strong, it won't twist and as I'm replacing it anyway it was ideal for bracing the door aperture ( sort of recycling!), I just ground the paint off either side of the inner door frame and tack welded it in- don't overdo it as you will want to take it off as cleanly as possible to minimise grinding/cleaning up this visible part of the car.
I replaced the boxing section leaving the floor pan in place, and when all of the outer sill parts were securely welded in I removed front and rear floor pans,beware when cutting out rusty sections,you may cut out a little more than the new panels may cover, needing a bit more metal to be let in, the rear floor pan on the drivers side had rotted out taking 1/2" of the floor pan near the rear spring hanger. A good tip I can recommend is to get 2 pairs of ramps which get the car high enough off the ground to give really good access to the sill/underfoor area-it made my life a lot easier, axle stands are not high enough when doing work on this area I think.
Read up on nams query in this section,he's doing similar floor pan repair-and go through members experiences on the same for hints,tips and pitfalls of the job![frame]

[/frame]Pic shows the sill trim section being used to brace the door aperture before cutting out the boxing section.