EDITED with new info
Stan, yes, now that you've mentioned it, 63 provides typical tail/parking light brightness which is only 3 CP. Stop and signal lamps are usually 21 CP. If your turn signal lamps are single filament, 1129 (21 CP) should work. If they function as both parking and turn signal, then 1158 should work. BUT -- read on.
I checked the bulbs in the after-market tail lamp assemblies I pulled off the Jimmy. They're dual filament, but instead of 1158, they're 1154. I investigated, and 1158 has what's called "in line" posts on the side of the bulb base (to twist and lock into the socket) and 1154 has offset posts (one higher/lower than the other). Otherwise, I presume CP is the same for filaments on both. So, if the slots in your sockets are in line, use 1158, otherwise go with 1154. I'll have to check one of the 1129s I have sitting around here and see if its posts are in-line or offset.
Edit:
OK, the 1129 has in line posts. I couldn't find anything about a single filament bulb with equivalent CP and offset posts, but such a bulb might exist, unless the offset treatment is only found on dual filament types. I have a feeling that your Plymouth has a dual purpose parking/signal assembly and would take either the 1158 or 1154, but if parking and signal lenses are separate, then 1129 (or its offset counterpart) and 63 should work.
[this post was last edited: 11/3/2017-18:09]