For some reason I've always been fascinated by the .38 Super, but I've never coughed up the money for the proper slide.
The .38/9mm frame theoretically has a different feed ramp shape, but there's such a wide variation among manufacturers it's lost in the noise.
.38/9mm use a different ejector. They're cheap and many different configurations are available to play with.
The magazines are different between the .38/9mm and .45; feed lip width, mostly. They're the same size in the main body.
The slides are different between the .38/9mm and .45. The width of the slot where the case head rides onto the breechface is narrower on the .38/9mm. Some people have had good luck using .45 slides with the small cartridges, but Colt felt it required a different slides. There may be a third breechface for the .40-based cartridges.
There were some other minor differences, like the smaller diameter firing pin used with the small cartridges, but a lot of .45s use that nowadays.
Major factory calibers are: .38 Colt, .38 Super, .38 Special, 9mm Parabellum, .357 Sig, .40 S&W, 10mm S&W, .45 ACP. Yes, rimmed .38 Special, with the bullets loaded flush with the case mouth like a Nagant. Colt sold them for target shooting several decades ago. .38 Colt is the base cartridge for Super, and pretty much obsolete.
Some aftermarket calibers are: .45 Super, .460 Rowland, 9x23 Dillon, .41 Avenger. The Super is just a high pressure .45, the Rowland is ballistically equivalent to a .44 Magnum (take THAT, Desert Eagle fanboys!), the 9x23 was designed around "high power" pistol shooting rules.
With a little "adjustment", 7.62 Tokarev can be made to work. Search "1911 Tokarev" to find Tok'11's threads on it.
1911-based pistols are made in .50 GI and .357 Magnum, but the frames are cast with larger grips to accomodate those cartridges. There are also some "double stack" .45 frames floating around; many internal bits needed to finish one of those are rare and expensive.
Several 0% builds and caliber conversions at the bottom of this page: 1911 Internet Thread Archive