I know there is a lot of debate on this, but the 69 convertibles from Van Nuys came with gray primer on the bottom and the Ohio plant had red oxide, although there is one member on here that has a body colored floor from Ohio. I guess it depends on what you believe to be true. For me, it was just not wanting a black bottomed car, or the gray primer either. Body color looks nice and will accentuate the detail with all my new brake and fuel lines, not to mention after putting a new floor in the car with new bracing, that I didn't want it to be all covered up with undercoating.
I did go thru some pictures yesterday of a red RAIII convertible (almost perfect show car, that was featured in Hemming's Muscle Machines a few years back). I know the owner of that car and although I didn't have the best picture to see the exact area, he did have the black firewall transition near the seam of the floor to the gray primer, so I'm going to keep it where it is.
Thanks for the input and I appreciate your opinions a lot.