I just saw a Springfield Armory complete top end in 38 Super for sale. I believe it was in the FAC catalog www.gunsnstuff.net Everything you need to put on your frame. Of course, slide may need some fitting to your frame rails,etc.
Except for the possibility of feed ramp variations, the only thing needing changed on the frame, would be the ejector. The 38 and 45 ejectors are different. A complete upper change consisting of slide, barrel, and internal parts is necessary. At one time, Colt factory complete lowers were available, and they came with both ejectors, so you could use them with 45, or 38/9mm uppers. I bought 10 of these from CDNN and built up 45's, 38 supers, 9mm, and one 9X23, and all ran fine, with no feed ramp rework required.
As I recall, this was in the early 90's, and the genuine Colt factory frames were selling for 169 bucks, for a purchase of 3 or more. They came with Colt hard case, Colt outer sleeve/box, manual, two ejectors, and I believe the slide stop was included.