Thanks for asking our advice and welcome to the forum..
You could run a fired and sized case (before case mouth belling and, of course, without bullet or powder) into the chambers to see if a 38 Special case fits. Then bell the case mouth, load a round with a GENTLE crimp (just enough to remove the bell) and see if that fits. If you want to apply more crimp, do that and check the fit again.
Then if that did not confirm the chambering, I would go to a gun store, go in and ask the manager if I could bring in a gun and see what ammo fits in it. See if factory ammo fits. Of course, you are probably obliged to buy a box of whatever does fit, just out of politeness.
Congratulations on a wonderful find. (Of course, since it was unfired, it obviously was not used in a murder unless as a club. Your Mother can rest easy.)