Won't hurt to ask, but doubt if Ruger (or any other manufacturer) will make you a non-standard bbl. length. S&W and maybe Colt once did, but no more. Well, heck: I know danged well that Colt did, at least on the SAA: that's where those Buntline Special guns came from. And we've surely all seen the famous letter from Bat Masterson wanting a 4.75-inch bbl. before Colt routinely made that length...
However, in this case, if I wanted a .32 when I could have the gun in the more effective .38 Special, I think I'd opt for the nominally three-inch bbl. to get the velocity up to a respectable level. For what it's worth, I think I read that Geco's wadcutter is among the hottest standard .32 Long ammo. That gun takes the .32 H&R Magnum, though. I'd still choose the longer barrel.
If you get the .32, let us know how it does, especially if you take small game with it. Of course, it'll kill venomous snakes. It's mainly the two-legged threats and wild dogs, etc. that leave me thinking the .38 is normally the better choice in a small revolver.
Lone Star