+ Basically, a red oxide epoxy-based primer sealer. So, the final look will be smooth and slightly glossy not like you have seen for rattle can red oxide primers. Tone and tint will differ depending on when the car was built and the tone/tint can often differ between the two applications. One from approx. the firewall rearward and the second one from that starting point forward.
That was followed by overspray from the exterior body color application to the body and in the rear wheel wells, Black from the engine compartment application and finally the pinch weld black out before the front fenders were installed all the way to where the rear valance would have been pulled into the unibody. It was hung from the taillight panel just before the car was painted but not pulled into the body until after the process
Invite you to take a look at all the pictures posted on the Concours site. Not an advertisement, just trying to help. Joining is not required to see the general question section organized by year. But you would need to join to see the articles such as 1966 San Jose Undercarriage Details or the unrestored car section
+ "Color" of the drive line would be plain bare steel. Nice smooth and fresh. With a heat line/stripe from one end to the other from forming the tube. Cast steel yokes at each end, so they will look different from the driveline and each would have had brightly machined surfaces in the appropriate locations and finally a dark welded where the yokes were attached to the tube. Of course, there will be bluing on the tube from heating the metal (just like on the edges of the heat stripe on the tube) near where the welds are. This can be done with gun bluing repair fluid as well as using it to create the heat stripe and darkened welds
+ Third member would be a different red oxide epoxy product - often slightly redder (floors are often a muddy red) and more consistent in color through the production year. This was applied to the whole third member inside and out then the casting was machined so you would see those details and highlights on it ans the pinion retainer. Some of these spots are different than on a 9"
If looking to reproduce the original look you will not find anything ready made out of a can. Will need to be custom made. To show the variation of just some of what was sprayed to the floor sections during 66 production at San Jose here are three examples. The first couple showing muddy brown examples (different cars) is closest IMHO to the most commonly found. Have a fair number of pictures of floor examples for that year and plant as well as a few sections that have been cut from unrestored cars from the floors
Now some overspray examples
In this one the pinch weld black out has been cleaned off. On this example the amount of body color overspray is massive compared to som others. Must have been a shorter or younger (willing to bend over a bit more) painter. Arrow shows the red oxide color of the floor under all that red paint
Pictures to show the pinch weld black out overspray applied after the body color
This one is another red exterior car. Even with the low contrast between the red oxide and the red you can still make it out just inside the black overspray
Don't use the pictures to figure out the original color as camera settings, lighting and monitor settings vary too much to get a real true example of what they look like in person