Mine cycles anything in 38 cases like they were made for it, RNFP, SWC, XTP, they all work in both 38 and 357. Some rifles will and some won't, you need to try it for yourself.
If you've got thousands of 38s you may as well use them if your rifle likes them. As already mentioned, Keith's 38/44 load will do just about anything the 357 will, but be extremely careful with that quoted load from magIvr, 13.5 grains was the load with Hercules 2400, not Alliant 2400. 13.5 grains is above book maximum even for 357 cases let alone 38 cases. I have used 12 grains behind a 158 grain in a 38 and had no pressure signs, and would think that would probably be a safe place to start.