Try placing the new carpet face down then center the old one on top also face down, this keeps the nastyness off the nap
Mark the hole for the e-brake with a marker, then cut a smaller hole in the new carpet, the rest is easy from there,
If you go over to the fox forums, better yet, I'll just move this,
It's also a good idea to checkout the floors for rust/damage and maybe add some sound deadener/insulation.
don't cheap out on the carpet Get one with a factory padding and pile
I also would put some dynomat or similar heat and.or sound insulator while you have the carpet out.
Even some spray on products help
I've done this twice recently after damaging the first one.
Both times the mass back carpet (worth the extra money).
Don't bother matching it up on the old carpet, I found that to be inaccurate.
Get it in the car and use a really sharp knife to open up holes as needed.
After it's where you want it, poke upwards through the seat and seat belt bolts.
Don't be surprised that the new carpet is about 10% bigger, you are going to have to trim the front and the back down to fit.
Be careful and patient with the knife, it will run if you're impatient.
Save yourself the headache of having to wait for parts by purchasing the lower trans boot, might as well while it's apart.