7.62 x 39 AR

[Tbat]

So am I correct in understanding that the only things that I'd need to order differently when building my 7.62x39 AR15 are the bolt, barrel and magazines?

Yes, that should get you where you are going. You may need make sure that your intended muzzle device will work with .30 caliber projectiles and be the proper size and thread pitch for your 7.62 barrel, as well.