KKF (Kurt's Kustom Firearms), a well known operation in Florida (sadly no longer with us due to a motorcycle accident a few years ago) made many of these custom uppers. I have one of the first.
Built on a M4 flattop AR upper, Kurt took a new 16" Bulgarian AK-74 barrel (chrome lined and designed from the ground up for the 5.45x39 cartridge) and mated it perfectly to the AR upper. He drilled a gas port in the midlength position as well. We then took a Young's National Match chrome bolt carrier, key, cam pin, and firing pin and got an Alexander Arms .221 Genghis bolt - AA did the first 5.45x39 uppers many years ago, and these bolts are top-notch.
A YHM Phantom flash suppressor, YHM Spectre Length Diamond FF handguard, adjustable gas block with midlength gas tube, Badger Tactical charging handle, and Magpul MBUS sights rounded it all out.
I've got about 400 rounds through the upper. Other than when I screwed around with the buffer weights and springs, it functions flawlessly. I am including a Spikes T2 tungsten powder buffer and CS blue extra-power spring with it since this is the combo that runs most reliably. Accuracy is incredible - honestly, I'm shooting 2-3 MOA with this using surplus spam can ammo - yeah, that good. Must be the Bulgarian barrel.
I am also including another adjustable gas block with midlength tube - this is a railed block in case you decide to swap the other one out - I switched them out because I wanted to use rail-height BUIS sights.
Meticulously cleaned and maintained.
Now, there are some scratches and dings here and there, mostly on the gas block from my ham-handed attempt to remove it without using something to keep the tools from marring the metal - I've filled it/covered it with black marker and honestly it doesn't look too bad. The replacement gas block doesn't look as bad. I haven't "set" the set screw yet as some people may want to tweak the gas settings - but my suggestion would be once you find the sweet spot, use some blue loctite and set the screw so it doesn't move its way out after lots of rounds.
I am including (12) 30 round mags - 4 of them are Gen 1 C-Products mags, 8 of them are Gen 2 C-Products mags. All work flawlessly, thanks to the upgraded springs and white followers in them - honestly, they work great and I've had NO problems since I upgraded them.
I've got close to $1150 in this upper and accesories and mags. I'm asking $750 for the entire kit and caboodle. Might consider trades, though I'm not really in need of anything right now other than good 5.56 ammo, maybe some optics/red dots - who knows?
If you are local (Central FL) I can meet you and unload some ammo on you as well - $150 per spam can of 1080 rounds.
Also have a complete lower (Stag) that I might sell as well - has Foliage Green MIAD full pistol grip, CTR stock, all internals. Will do a package deal for the upper and lower.
Also have a Vortex SPARC red dot optic that I can include for $175 as well.