Welcome to the forum. Concerning red-oxide, there really isn't a correct formula as it could vary from plant to plant and during a production year. Red-oxide wasn't the only primer color used and a single car could have multiple colors/shades of primer as it went through the coating process.
Best thing to do is post when/where your car was made to get the best feedback. Of course, if the underside of your car is original, all you need to do is clean some areas like up in the transmission tunnel to get a good sample to color-match.
As far as the type of primer, if you're having a shop do paint/body, you would need to discuss with them. If you're doing it yourself, there are several options out there with epoxy primer being a common recommendation, something like PPG DP-74LF. Of course, where you live may influence the type of paint/primer available for purchase.
One last thing... be sure to use the search tool. Lots of previous discussions about this topic here.