I've got everything I need now to create a full diff of the FalloutNV.esm FormID's except one thing.
A pre-1.3 patch version of the file.

If there's a util out these that can read the fallout SIS/SIM/SID files that would be perfect.
(I did download one program that looked promising but it's for HL2 apparently, and the website is in Russian)

If there isn't a program that can read the files then my only option is to reinstall.
I'm reluctant to do that as my Broadband is now shaped, so it could take days to get the system back up to date if I stuff up.

So my questions...
1/ Is there a SID reader compatible for falloutnv?

2/ If I need to reinstall, are there any additional steps I should take to avoid a lengthy update via Steam?
(I'll backup all of Steam\SteamApps\* before the re-install)

Edit: It seems option 2 is a non flyer.

The install setup on the DVD is similar to steams restorebackup program.
They both require a live connection to steam to run, and verify the files before unpacking from the DVD/backup.
If the files are out of date then it goes directly to the newest ones on Steam.