The undercut is relatively easy...it is just grinding, blending and reblue.
The chain link texture is a bit more problematic...it usually requires a fixture to hold the frame while it is being milled as you'd want all the scallops to be aligned and of uniform depth. Pretty easy if you have the equipment and understand the pattern, but I wouldn't think every gunsmith would be equipped, or want, to do it.
Also remember that the Chainlink of the STI Trojan has been softened after it is cut...otherwise it would be closer to the Ed Brown Chainlink
...because the journey is the worthier part...The Shepherd's Tale