wcoats - the best way IMHO to modify your Saiga to take standard mags is to purchase a bullet guide and install it. This will take a bit of drilling and tapping for the screw, but as long as you take your time and are careful you should be just fine. Then shave a bit off or your magazine catch a little at a time until the new magazine fits securely. This can be done with a file or a dremel. Again, just be careful and don't rush it.
Oh yeah.. before you order a bullet guide be sure to open your rifle up and check to see if you have a flat or round trunnion.
jonfish -
Here is a pretty handy video that I found helpful when I did my conversion. Nice to the point and easy:
http://www.vimeo.com/2787027
I bought everything I needed from Dinzag and Carolina Shooter Supply.
Use this little checklist to make sure you keep her legal:
http://thegunwiki.com/Gunwiki/BuildAkVerifyCompliance
As long as everything else you use in the conversion is US Made you should be able to use import mags, and maybe even an import forearm/handguard.
I still used the cross-conn site because the pictures do come in handy from time to time when you need to check something out a bit closer.
One handy thing I did that none of these videos shows is a trick to getting the BHO spring installed. (Bolt Hold Open)
Take a piece of dental floss, run it through the hole in the spring and through the hole for the back FCG pin, then tie it off into a good knot. You can use this to pull the spring tight until you line up the pin, once everything is lined up, cut the dental floss and push the pin on through.