I have one. This is what I should have done.
Get the KNS protector some where. Get some spare paddle in various sizes. Get some real Colt burst kits, make sure the kits are complete (if you want safe / semi / auto). Sturmgewher is a good place to start looking for all the above.
Forget about buying stuff that’ll work with the link. Forget about getting a low shelf lower. Forget about getting a Young Manufacturing carrier, forget about getting SP1 anything.
Low shelf lowers, I had to get milled further. YM link compatible carriers, had to get milled (slightly) to work. Get either one of those two, only if you actually want them. Don’t get them if you think it’ll be drop in plug and play. I ain’t knocking anyone. I bought a machine gun directly from Dan Young, and got a personalized tour of his machining area. Great guy and easy transfer.
If you choose quality uppers, lowers and carriers (within spec), you will be fine. You can get the lower and carrier milled to work with the link. Start looking for someone to do that for you, assuming you do not have the proper skills and tools to do it yourself.
Sure you can get the Sig and less machining on the bolt, but then you have a Sig upper. I would only go that route if you want a Sig upper. The saving in machine time (money) is insignificant.
What I would do. Get whatever quality lowers you want, because they’ll be (realistically) married to the link. Of course not legally, but if you ever sell the link, most likely you’ll offer the link compatible lower with it as a package deal. I bought some low shelf lowers and they still needed some material taken out. So I came to the conclusion, get whatever I want and get it milled out.
Get whatever carrier you want and get them milled. I highly recommend getting a gas adjustable carrier. Once again, most likely you will sell the carriers with the lower with the link, if / when you sell.
It maybe less frustrating to get several done at the same time.
No offense to anyone reading this thread. OP, you spent $15k on the link, you have the money to get it done so you will not have to worry about it again.