I sent an email to Starline, inquiring about the difference between their x23 and Largo brass, they replied:
"The main difference between our 9mm Largo brass and our 9x23Comp brass is the hardness of the head of the case. The 9x23Comp get hit a lot harder during the heading process to harden the head for better performance with high pressure loads. It also uses our tighter “Super” primer pocket while the Largo uses our standard primer pocket."
It's not apparent from this reply that they see a dimensional difference between the two, and the only reamer rental place I found so far just calls out 9x23.
http://www.9mmlargo.com/books/9x23.htm lists 14 different cartridges as "9x23", including the .38 Super Comp, never mind the case dimensions.
I'm now thinking, re-chamber to 9x23 and load to, oh, say .38 super pressure, and measure the rollers a lot, should work out.
Never have been able to find out what pressure the Largo was/is loaded too, so assume less that 9mm, FWIW.
Reading around on the 'net, seems a lot of people shoot the .38 Super in the 9x23 chamber without ill effects, also FWIW..