Installing new headers/pipes without removing muffler

[Steve Tinker]

I'm just about to install new headers and cat delete pipes (but retain the rear muffler) on my 2001 S.
Before I squeeze my old bones under the car, I need a couple of pointers from people who have already completed the installation.

I assume that I can remove the headers first and then pull out the cat section of the exhaust system without actually removing the standard muffler (at least I hope I can - I don't want to remove the muffler on my own if I can help it).
Looking under the car, will I have to remove the 2 x diagonal brace rails and aluminium plate below the gearbox to help with the removal / installation of the pipes?
The plan is to a) remove the rails and plate, b) remove the headers - no O2 sensors in Oz, c) remove the cat pipes / O2 sensors after unbolting at the muffler.
I assume the installation (as they say) is in reverse order.
And can I reuse the header bolts - assuming they come out OK?

Any handy hints greatly accepted.