Thanks for the reply Kenwood. I never thought about the white paint yellowing with age. There is paint on the shell, as I see some stray white paint on the shell near the bearing edge. It is still white, maybe because it has been covered by the head all these years?
I just ended up wrapping a poplar shell 16" floor tom. I primed the outside of the shell with white primer just to be consistent. The Antique White Pearl from Precision is opaque so I probably didn't have to. The color is a close match but it is not as "yellowed" as the rest of the kit. The pearl/swirl pattern is an exact match. I'll post a picture when I have them set up.
I also believed I solved the mystery of the cymbal mount, when working on another MIJ kit recently that was exactly the same construction as the subject of this post. The mount was missing a piece! See the picture below. It was missing the "dog ear" that is the same piece that is found on rail mounts that holds the L-arm/tom arm and locks the angle in place. The piece for the cymbal arm just doesn't have a protuberance on the back to lock into the gear/clockface of the rail mount; otherwise it's exactly the same. This piece sits directly on top of the piece in my initial post. It seems to be for 3/8"/9.5 mm L-arms, but when I inserted a 3/8"/ 9.5mm cymbal arm into it, I couldn't get it tight enough to hold. No matter how much I tightened it using the "baseball bat" handle, the arm was still loose. Maybe my dog ear piece got stretched out or maybe a 10.5mm arm would work better. Anyway, another solved mystery!