Well, that bottom one looks just like every other one I have ever seen ( that style, anyway ).
Spun shaft ends...?
And I looked a quite a few when attempting to put a "Door Disassembly" Thread together. Still working on it , tho...
The real bummer is... you did not get the Good "Mexico" parts. Seriously.
When you get the old one out - if not already, pop the socket top and see what CB it has.
I have seen 4 types.
Your remarks give away your newness to good old GM aftermarket elec. stuff. Altho, I realize you are a fine mechanic, nonetheless, all the more, what w/ the muffler back knowledge.
Have you given any thought what fasteners you intend to use?
If going 1/4-20, you'll have to drill em' out slightly.
I did that, as 5/32 and 3/16, whatever I tried originally, seemed so light, allen wrench size sooo small.
and riveting was a REAL HASSLE the 1st time a decade ago. Grinding, etc.
I can direct you to the correct area of our build if you like. Door stuff is in the last few pages...