Unfortunately, the barrel measurement seems to be true. Since I never measured any while in Iraq, I had a friend do a measurement on one in January 2009 shortly the issue popped-up and it seems the case. TheAKForum member "Jeff21" cleared the issue up quite solidly with some great photos - one of which pretty well sealing the deal on the US barrels being too long and the actual barrel being 21 3/8":
It's really a minor detail for most folks as there's not going to be an absolute 100% clone with these rifles, no matter what you do. If you want to get into particulars, the barrel issue is something like the difference between having a 75% perfect clone as to maybe an 80% perfect clone when you factor in US parts, receiver, etc. Who really cares with such differences. It's a unique enough rifle in its own right. And, as someone pointed out, it gains you some FPS in ballistics which is always good. I tinkered with one in Iraq for a few weeks and personally never liked the way it felt. It just seemed like a bastardization of a few variants of Kalashnikovs and never really satisfied any of them (ammunition of an AK, barrel of a sniper, receiver of an RPK, too long of a magazine for use, etc.). But definately unique.
As mentioned earlier, you're good for using the existing rear sight as-is. The numbers in what we now call European numbers (1, 2, 3,...) is right-on. The Iraqis didn't do their rear sights using what we now call the Arabic-Indic style ( ٠.١.٢.٣) numbers. (Vlad - not "Farsi" as that's Iranian

).
I agree and think you'd also be safe with a 42XXXXX for either 2002 or 2003 (which is probably the most commonly found years for the rifle, it seems). Vlad and a few members on the other site were doing some great number/year collecting and have some good examples (except the "102000 range on a 1998" one that was in question - that's actually an Iraqi Tabuk rifle if you look at part of the photo at the upper handguard where the grenade sight if it's the one on the forum photos).
And for those wanting to do one of these unique builds but finding yourself on the fence due to the interesting "circular hole" type front sight base, no worries. The Iraqi Tabuk DMR was also been manufactured with the "oval hole" pattern, as well, but the "circular hole" seems to be the most commonly seen ones.