[RWebb]

I would put down some sound deadener - use it in strips or squares over 1/4 of the floor area to save wt. or entire area if you don't care...

on top of that, you can use a so-called Mass Loaded vinyl (MLV) product (again I encourage you to sic some students on how it all works, esp. any that are interested in the acoustics branch of physics or bioacoustics over in the Biology Dept.)

the above is what I am doing, except I only removed part of the factory deadener instead of adding more - the MLV can be lifted out to save some wt. for AutoX or track use

NEVER use a roofing material inside the passenger cabin.

to make it a concoursmobile, but not one that has modern levels of performance, use coir or horsehair (search on those terms; thread active this week)

BTW - buy Frere's book on the 911 and study carefully - it has tons of info in it.