If I wanted to build on one of those Russian kits out there minus the hard to find barrel and wasn't worried about perfection couldn't i use a barrel from KVAR made for a 90 degree block and put a 90 degree block on the gun with a tube and piston from a 74 if necessary?

You could, but why would you pay the premium for a Russian kit if you're not going to build it as intended? I'm going to assume that this would be an AKM kit, in which case there are plenty of barrels out there that will work with it without having to resort to a '74 pattern barrel. Such as the newly imported Polish barrels.

Who is importing Polish barrels? I thought there was a ban on importation of barrels??
Did I sleep to long last night, & they chance the laws while I wasn't watching?

I'm not really concerned with cost or originality.  I would like to build a underfolder off a Russian AKM kit and I want to use the abosolute best barrel that I can find.  I scoured the Internet for a original Russian barrel and I am skeptical about the Romy barrels with Russian marks.  What do you recommend?

There's a ban on importation of "machine gun" barrels. The barrels being imported from Poland are new and have never been installed, so therefore they're "sporter" barrels and importable.

http://armsofamerica.com/polishfbradombrandnew762x39coldhammerforgedbarrelbuyanyv-projectproductpartskitandorqty3andreceive1000offeachbarrel.aspx

I understand that you're not concerned about cost or originality, but there's no point in spending more money on parts that offer no increase in quality. Russian parts have the most value when built as intended, and since this isn't your concern you'd be better off saving money and getting a Polish, Hungarian, Romanian, etc. kit which will serve the same purpose.

I assume by "absolute best" barrel your main concern is cold hammer forged? In which case there's zero evidence that a cold hammer forged barrel is "best", especially with a semi-auto build. AK-Builder barrels are typically across the board more accurate than combloc barrels according to my own experiences as well as other's. There are obviously people that disagree with that, yet they can never show any evidence of the contrary. Furthermore, AK-Builder barrels have been shown to have the same hardness as factory CHF barrels (something that was assumed to be the opposite up until recently).

The only reason to find an original Russian AKM barrel would be for "correctness", and not for having "the best". Since your intent isn't correctness, again, spending the premium on that part would be an exercise in futility.

Thank You for that link. I'm just getting back into building the last kit I built was right after the ban. I thought I was going to have to build on a US barrel.

You're welcome. Atlantic has them as well now. Also, there's absolutely nothing wrong with a quality US barrel.

Got one, thanks.