My conversion was done with a Clark Custom kit by Schiltron Munitions in Wasilla. I don't reallyknow anything about the polymer guns except they are total drop in. It isn't just a "Wild West" thing as far as I know.
http://www.clarkcustomguns.com/rowland.htmI am far from an expert but here's what I think I know.
The 1911 .45 has the comp to slow down the recoil cycle a bit as I understand it, the "no comp" conversions were battering the frames. I don't know how a comp helps with that except weight-wise? Very pleasant to shoot in any event.
A kid (former Marine, I get to call him that) here at work ordered a kit for his G21, I can give a report when I see it, not sure if it has a comp or not. He runs a 1" comp on his G21 now for some reason so he doesn't care about the added length.
As far as changing from ACP to Rowland, for my 1911 I don't have to take the comp off the barrel, I just disassemble the gun more or less as normal as I recall. When I get home I'll do it and write down the steps. It only took a couple minutes as I recall. But I bought a complete gun so I don't have to "change", I just grab my standard 1911 when I want to shoot it.