If you want ANY custom work on a 1911, I can recommend, without hesitation, Wayne Novak in Parkersburg, WV. He has an FFL, so you can ship directly to him, and he can ship it directly back to your residence legally under NC law.
His shop is one of the best 1911 custom shops East of the Mississippi, his prices are reasonable and his turnaround time is quick.
As for custom work on a Sig, I don't know much about that. I'd suggest using a Sig-certified armorer though, because the Sigs are pretty tight-tolerance guns and you don't want just any hack machinist with a Dremel going at our Sig internals...