I have a set of Lee .357 dies, the only die with both .38 and .357 marked on it is the Resize/Deprimer, this die will work on both. I know the Seater die will not work with the .38 but I believe you can screw the Expander die in enough to expand the .38 but depending on your press, you may have to take the Lock Nut off.
I had to get a set of .38/.357 dies to load .38's. Couldn't find any Lee in stock where I shopped so I got the RCBS. RCBS comes with a spacer for loading .357, I believe this is used on the both the Expander and Seater dies.
I have never loaded .357 so not sure and don't remember what the instructions call for with the spacer.