1911 10mms: They cannot easily be built up on .45ACP setups--the main problem is the ejector. The 'heights' of a .45 ACP ejector and 10mm obviously aren't the same--so a .45 ACP ejector is too short; it might function (there is a gunsmith who used to try this), but it is not recommended.
Further, there is the issue of type of feed ramps (on frame, or integrated with the barrel). Generally, good 10mm setups have a feed ramp integrated with the barrel, so the frame is incompatible with a standard .45ACP top end.
Zundfolge's post covers the issues pretty well.
The length of 10mm and .45ACP rounds is nominally the same, so it really is just an issue of tweaking ramps and feed lips. It used to be that .40S&W mags had a shim at the back--I haven't looked at any recently. Other than raceguns, I've never understood why one would own a .40 Short & Weak in 1911 frame, save for the sheer love of 1911s. (OTOH, if SA gets that Micro frame running in .40, that might be a real neat one.)
OTOH, the EAA Witness (and some others) can just be a top end switchout--pull the .45ACP off, put on the 10mm. I have one of these, and it functions perfectly. This package is a cheaper way into 10mm: If one can find one of the Elite Match .40s (rare) and convert it, or the 10mm Elite Match (even rarer; get on the waiting list), This can make a nice convertible.
Despite the forum discussions about Kimber QC, the 10mm Stainless Target II I bought this summer is simply wonderful. I put it through a typical break-in with FMJs, and from round 50 forward, these were reloads--180s running about 1000 fps (just above a target load). One night we did some club competition at 50 yards, when I was at about round 350 or so on the break-in. Although I had never shot handguns at 50 yards before, I could hit a 12" gong in measured / sustained rapid fire. and reliably hit bowling pin 'heads.' That's not a testament to my skills, that's a testament to the ST II's accuracy. It routinely does 1.25" 8-shot groups at 25 yards, and not infrequently without a flyer. It did need the 500-round break-in, however.
IMO, 1911s and 10mms (and that EAA Witness Elite Match) are matches made in heaven.
Jim H.