First welcome to the site - Hope you find the support and information here helpful in your restorations endeavours
There is not "out of the can" color or tint that will likely match any of the original red oxide colors applied to 67 Mustangs and Shelby's. If you read the article in the library you will also be reminded that there was two different applications on the undercarriage (one firewall rearward followed by firewall forward) so I suggest you read that document as a start
Many over the years have chosen to start with a base of Ditzler/PPG P74LF (an epoxy based primer sealer) then have the paint shop tint it to match the original color found on the floor pans and also the front frame to get both colors. Out of the can it will be too red and it needs to be a muddier color. There are a fair number of threads with pictures of examples from original car but would suggest, that if you have already removed all your original color focus on other examples available built at about the same time at San Jose as your car.
One of many threads you can find using the search feature - hope this helps
http://www.concoursmustang.com/forum/index.php?topic=12069.msg73125#msg73125