The trim clips on a '52 & a '54 I disassembled were all like the rusty one in this photo. There were threaded stud fasteners only at the ends of the sections and pretty much sized to fit. I was told by Lou Retzer that my clips are the same as '46/'48 Plymouth clips which I found at Restoration Specialties & Supply in PA. Give them a call for a great catalog, 814-467-9842
I saw the spring type clip (push in) for the first time on a piece of used trim on ebay this winter. I cut a good section out of a piece of bent trim and sent it in with the ebay photo to Restoration Specialties to see what they could come up with, and I also asked what they had for the threaded end clips in case I wanted to replace my originals.
Left to right in the attached photo is my original style (rusty), #2444-CLP 46/48 Plymouth Body Belt @ $2.50 each, #2789-CLP Moulding Fastener Bolt 10-24 x 5/8 and #B1108-CLP Wire Clip 48 Chrysler Hood Side @ $1.25 each.
My understanding is that the tang on the backside of original style is spread from the front, tightening the clip to the body and then the trim is "snapped" onto the clips.
I bought a few of each to try but am not that far along so I can't comment on how good they work. They all seem to fit the trim section well.