There was a bit of a cottage industry in the late 70s (?) and 80s with gunsmiths putting Colt barrels on S&W or Ruger revolvers. Supposedly, the Colt barrels were more accurate and "harder hitting" (no, really, that was the argument) than the others, but some folks wanted to keep the operating characteristics of the guns they were used to using while gaining the advantage of a Colt barrel. Thus Smolts and Cougars were born (SMith + cOLT or COlt + rUGER -- COUGER/COUGAR, close enough). As a competition (PPC) revolver shooter back in those days, I handled a few of these guns, and remember shooting one Smolt. It functioned perfectly, and accuracy did seem to be better than the stock S&W from which it was born, but that could also be attributed to the glass-smooth action job that was performed at the same time as the re-barreling.
They were custom guns, they looked cool, they were fairly unique, and if done correctly, they shot REALLY well; good enough reasons for any conversion/custom handgun to exist, I'd say. I've never heard of or seen one quite like the OP described, above, but I imagine there were many variations on the theme.
Here's a Couger (Ruger Security-Six .357 with Python barrel) photo I found on the 'Net and re-hosted:
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)