I already own a Noveske "flaming pig" that I will have silver soldered on.
It's your dream gun and not mine, but I'd suggest thinking that over a bit. I have a KX3 on 10.5" barrel and I often wonder if it even makes much sense in that application. The KX3 serves two main purposes, 1) increase back pressure to help short barreled guns cycle reliably, and 2) reduce some of the blast and project it forward. On a 14.5" gun you have no need for number one. And in fact you are arguably adding something to the mix of port size, barrel length, gas system, that may be a negative. The KX3 as you know since you already have it, is neither small nor light. IIRC it weighs in at 7 ounces and some change. That is nearly half a pound. It also is over 3" long. There is a pretty good argument for just going with a longer barrel instead of a pig. 7 ounces is a lot of weight to put right at the end of the muzzle. For what it is worth the pig will make 16" on a 13.7" barrel but its not advised by most folks who are in the know (nor is the 14.5 w/ the KX3). See:
http://www.ar15.com/archive/topic.html?b=2&f=130&t=183163 There is a very compelling argument that the KX3 just isn't worth the weight and length. Admittedly, it looks very cool. I'll soon be taking mine off of my 10.5" gun and going with a suppressor. On a 14.5" gun I would never consider using the KX3. If blast is a big consideration, get a real suppressor. If its not a big enough consideration to warrant a suppressor (even on of the minis) then use a flash hider and profit from not having extra weight at the end of the barrel.
As to your question of where to get an upper or a barrel. If this is your dream AR, remember the barrel is the heart of the gun. A barrel and the bolt carrier group are the the most important parts of having a good AR. Do not skimp here. I'd rather spend more on the barrel and sacrifice the fancy UBR stock, etc, than get a cheaper barrel.
If I were in your shoes I'd look at BCM for a 14.5" midlength barrel or upper receiver group. I might even get one with a FSP and chop it to have in effect a pinned low profile gas block. There is lots of info out there on how to accomplish this.
If money is less of a concern you could look at Noveske barrels including their stainless steel barrels if you want/need more accuracy.
https://www.rainierarms.com/?page=shop/browse&category=ar15/m16_barrels_noveske
What is the main purpose of this gun? How many rounds a year is it going to see? Those would influence my personal choice of what barrel to get.
