A very valid question, though the term "snap-in" pads (technically "snap-on" pads) is usually reserved for the older Bueschers that have posts on the padcup.
Conn resopads with their metal ring around the perimeter will actually (sometimes) snap in if the metal ring is just the right size. If sized properly, the metal ring will not go down below the rim of the padcup - so if the edge of the pad just next to the rim of the pad cup is very hard underneath the leather, then it is probably a resopad. A strong magnet will tell you if there is a ring there!
While a well-fitted Conn resopad may not require shellac to hold it in, I think it's a good idea to use a little as insurance should the pad decide to come loose. So it's a "maybe, maybe not" as to whether there is shellac there. You would want to heat the padcup prior to trying to remove the pad if you wanted to salvage the pad so you can put it back in.
The Ferree's replacement reso pads have flat metal resos that are relatively small for the bell keys compared to the reso size that you usually find with those large pads. I don't have the historical knowledge as to original resopad resonator sizes to assist further, though.
And congratulations on the 1945 10M. Sweet.
