Just want to confirm that you found red oxide color floor at the rear of the car, is that correct? Asking since, in 65 production at San Jose, red oxide epoxy primer sealer was not always used. Have examples with projected build dates of 2/10/65 and 2/18/65 that didn't use red oxide at the rear. Just trying to confirm what and where you found clues.
Also remember there were likely two different tones or tints of the red oxide applied to the bottom of the car. One from the firewall rearward and one from the firewall forward in that order.
Nothing straight out of the can will likely match. If you do a search you will find descriptions of mixes, additives and base products others have used.
Try words like " red oxide"