"I believe early .357 Magnum ammo was made with a large pistol primer and I should think that would make for an interesting and non-ordinary look."

I have quite a few different .357 example specimens in my collection, none of which have large primer pockets. But absent their original boxes I have no way to date them accurately. I do have some early .38 Auto cartridges and cases which have large primer pockets (USCCo), but again I cannot date them. While it is possible that some early .357 cases may have large primer pockets I do not remember seeing one. And I do not know what the benefit(s) of using large primers would be, as small primers seem to do a satisfactory job of powder ignition in the .357 case.