If you already have a SP101 in .32H&R, you can get a reamer, or pay someone who has a reamer, to extend your chambers to .327 length. The extraction rod will be too short and you might need a different front sight. It's about $100 for the reamer or the service, either way. I know this is common for SP101s and S&W 16-4s. You should consult a knowledgeable gunsmith on any other guns.
I've thought about reaming my cylinders for .327 but that was before Ruger offered my identical gun chambered for .327. It seems to me that it would be easier to just buy a new .327 and sell my 32 H&R Mag if I decide that I really want a 4 inch SP101 in .327 Federal Magnum. I suspect any future buyer would also prefer an official 327 instead of a rechambering.
That said, right now, I'm more interested in the Ruger Single Seven with a 5.5 inch barrel then the 4 inch SP101.