I have not seen any batch color under the car just the yellow looking paint. I had wiped it over with paint thinner and that's what showed up. Maybe after all those years and having the sound deadener over it that it has taken the gold look out of it. There was no batch or yellow paint on the wheel well side of the firewall
Looked again at your first pictures the the blue gray I was seeing in one picture appears to be your transmission
and under the black on your first torque box appeared to be a gray gray in contrast by this may be an older black application than had aged and over coated with black First post pic #4
After looking at your new pictures it pretty apparent that the yellow like color (not related to the trunk finish) was the batch color. As I've mentioned before with the addition of all the grabber and brighter colors introduced in 70 we saw a much wider range of batch colors due to the addition of all these colors. Have seen bright green, orange/burnt reds as well as the dark grays we saw in earlier years. When they happen to be close in color or tint to the exterior colors some assume that the cars were painted exterior color both top and bottom while on other cars the two clash like orange or yellow cars with light green undercarriages/floors
6th picture in your second set though does make me wonder what is going on or what you may have done during clean up since its either dried paint (floor color) that remained after your cleaning or something not factory is going on since it appears that the yellow is on things like fuel lines and e brake cables. Items not added until after painting. Can you explain in that picture?