Been there done that
I spent 3 years in Malawi as a volunteer. "internet" was a 9600 baud modem. So I collected tools, software, etc when in the UK, or from other volunteers/AID workers etc. ZIP Drives where my best friends - remember them?
Anyway, spent a lot of time fixing laptops with software issues, viruses, etc. So top tools needed were: Current AV software, Partitioning tools, OS + Driver disks, Common Application install Disks, doggy licence keys (cough!).
So go with a SysPrep'ed image by all means, but hardware (graphics, printers, gadgets) drivers may be your issue? The remote WSUS idea appeals - can you inventory before you go? Get them to run off a System Report and post them, just something. But you'll need to get the data off the machines before you nuke 'em, so a USB hard drive or two could be useful. I'd also suggest if possible virtualising the Applications (ThinApp?) - so no install required? An USB CD/DVD as well as the CDs etc of the OS, and common Apps, may be the only way to get them going.
But local hardware could be a mixed bag, and XP/Office 2003 etc may still be the right tools for the job - they won't have the drivers for that either though? CD/DVD/Floppy drives will be knackered - even USB ports may be too old? Take a working desktop you can use to plug in IDE drives to uprgade???
I'd really consider the suggestion of shipping the lot somewhere connected? Or take a Satellite Dish?