I have 2, right now, that I changed from .45 acp over to 9mm. No problem with the ramp. I have changed numerous .45 1911's over to 9mm, .40 S&W, 10mm, .38 Super with no modification to the ramp, and back again. .38 super, 10mm worked best with ramped barrels which require machining the frame and you can't go back to regular barrels without major mods. I also have a .45 that Converted to .10mm with no ramp work. You just can't load the Super or 9mm, or 10mm as hot without a ramped barrel. You do have to change the mags, ejector, slide and extractor. If you get the right slide you can use it with out mods for 9mm, .38 super, .40 S&W and 10mm. Same with the ejector and extractor.
I have a custom Para wide body right now that I changed over to 9mm for 3 gun that is 100% reliable .