Linky to construction article for the Airfix Saturn V:
http://www.ipmshawaii.freewebsitehosting.com/Newsletters/0907%20Jul%20Newsletter.pdf
If you get a recent reissue of the kit, the service module and interstage fairing dimensions have been corrected by Airfix. I believe that the service module has also been updated to the correct Block II configuration. I think the decals have been brought up to date as well, so you might not need the aftermarket sheet. I built an older kit, so I didn't benefit from the improvements of the reissued version.
The engines are a real bugger to clean up, so if you don't mind going to the aftermarket, Realspace Models makes the main engines wrapped up in asbestos lagging, which is representative of the launch configuration.
Hope that helped.
Neal