The Witness conversion is a sad story. I have the 9x25 Dillon chamber reamer, so I sent it and an extra .38 Super Witness barrel to a gunsmith to have it rechambered. He didn't chamber it straight, and the chamber came back egg shaped. Then I sent the reamer and a second .38 Super barrel to another gunsmith for rechambering, but he went too deep with the reamer and ruined a second barrel.....
I finally came up with a third .38 Super barrel and rechambered it myself, being very careful not to go too deep with the reamer. At the time, I had an old bench lathe that I didn't have a motor for, so I chucked everything up in the lathe and turned it by hand, getting several big blisters on my turning hand in the process, even though I was wearing a glove. At least I ended up with what I wanted, and learned that just because a person has a "gunsmith" shingle hanging out, that doesn't necessarily make them a gunsmith.
The 1911 was purpose built to be a 9x25 Dillon by a friend who is actually a gunsmith, among other things. I had purchased a 9x25 barrel and the compensator on ebay, and he built the pistol around that.
I used the .38 Super barrels because I had a couple extra ones (the ones that were ruined) for the large frame Witness. When I had this done, EAA was still selling both the large and small frame Witnesses, with the small frame being the 9x19 and .40 S&W calibers, and the large frame being the .38 Super, 10mm and .45 calibers. It was only later that they started importing the large frame in all the calibers.
I also rechambered a 9x19 barrel to 357 Sig, so I have a Witness in that caliber, too, along with one in 9x21, plus all the regular calibers the Witness is offered in. I have them in .22 LR, 9x19, 9x21, 9x23 Winchester, 357 Sig, 9x25 Dillon, .38 Super, .40 S&W, 10mm, .41 AE and .45 acp. The Witness is a good platform, easy to work on and fits my hand better than most pistols. The only other pistols that I have that fit as well are my Springfield XD's. (9x19, 357 Sig, .40 S&W and .45 acp)
Hope this helps.
Fred