In fact, it would be less practical -- 1st because you'd still have to have a barrel made, and 2nd because mags made to fit the 97B wouldn't work with the .40 cartridge that is the basis for the .357 SIG round. You'd have to find some EAA large frame .40 mags to even hope it would work. I don't know whether the breechface and extractor could be made to work on the .40/10mm conversion and the .45 slide. Maybe. With .400 Corbon, it would't be an issue.
Back to the basic point -- if you're looking for something other than .45 on a 97B frame, you're going to have to wait until CZ pulls one out (somewhat less likely now that Dan Wesson is offering a 10mm 1911-style gun), or go for an EAA gun.
EAA guns are the same basic design, and have a smaller grip. (I have one of the nicer Witnesses, a "Sport Long Slide", and have a 10mm Conversion top end. Its a nice gun.)