I had no issue other than a little fitting on the link when I converted a Kimber 1911 using a Clark kit. There was just a barely noticeable drag on the slide release lever when the barrel was unlocked, took me about 5 minutes to fix. The pistol behaves quite nicely with the Clark kit, a 20 lb recoil spring, Square FPS, and a 28 lb mainspring. Loads I was running a 255 hardcast at 1100 fps had about 5 to 6 ft ejection. I also put beefier springs in my mags.
My Glock 21 was a drop-in kit from Johnny Rowland, but I haven't shot it enough to come up with any real data, but I know it does work. I have been putting my range time into mainly a .458 Socom and a .300 Ham'r, and I really need to get back to that Glock. Besides the kit I purchased from Authentic 460 Rowland, I also put mag extensions on some mags and some beefier springs, too. I basically just function-tested it with some 275 grain Hunter Supplys at just under 1000 fps.
With it getting warmer, I'll probably dig that Rowland/Glock back out and start going through some loads just to see what's up.
In my Kimber and Glock 21, the conversion was pretty straightforward. The Clark kit did not fit my Ruger 1911 so well, so after installing it and looking at things, I didn't even try firing it, instead going .45 Super with it. I also have a Glock 21 set up for Super.
Try the Rowland, you'll like it. 255 grain Hardcasts are easily taken to 1200 fps, though recoil can slow recovery down at that speed. That and I just don't care for excessive recoil, anymore.
