Hopefully Tuner will chime in here and comment, but in my experience a ramped barrel isn't neccessary. Where you need a ramped barrel is when you start playing with super comp loads. It is still the same cartridge just loaded to a lot higher pressure, hence it needs the support around the case all around and the cuts (non supported) in a non ramped barrel are a safety issue. Remember the 1911 was designed for low pressure cartridges. In the supercomps the fix was a ramped barrel, in the 10mm the brass is much thicker in the web, and a lot stronger ( the parent was a rifle case).
On older guns the 38 super was headspaced on the rim, which is very small, and this effected accuracy. Newer pistols have changed to headspacing on the case mouth, not sure when this happened but the changed happened on the series 80 pistols. This is a valid reason to wanting to change barrels in older pistols, if done properly accuracy will almost certainly improve.
I am not a gunsmith nor do I play one on TV, but conversion of a 45 1911 into 38 super isn't practicle. At a minimum the slide must be changed, if you plan on a ramped barrel you might be able to use the frame, on a non ramped barrel the feed ramp on the 45 frame is larger to fit the 45 case and it would be welding bulding up the feed ramp project at a min, and end up costing more in the long run, with high probablity of feed problems in the final. I suppose welding on the slide could be done to convert a 45 slide also, but I think if you take this into a smith he is going to ask you why don't you just start with the right parts.
Slide details and assoiciated parts were pretty well covered in prevoius posts, slide, extractor, springs are all different.
On the 9mm conversion this is a path I haven't walked. I don't think the 9mm's feed as well as the 38 Super's, something about the length of the cartridge, maybe Tuner will see this and work on the tecnical explaination. It doesn't mean that 9mm can't be done, there are a lot that have been done in the past and Colt even made them. I also seem to remember something about magazines, when the 38 super mags are used isn't a spacer put inside the mag so the 9mm ammo won't slide forward, and cause feed issues? My point is there are a couple of small details involved in this conversion, and I would get the facts before I funded it. I know I have seen multiple 9mm original 1911's and none have the reliablity of the 38 Super. I also admit it would be a good range conversion, the cost of ammo drops to around half, but I don't think I would trust it as a carry gun. Once you have your hands on a 38 super, look into the 9x23 barrel this is basically a auto version of a 357 Mag, this round in 125 gr bullets and a mag capacity of 8 makes this an ideal carry gun round, very serious business.
