what octane should i be running?

my car is a 70 torino cobra with the N code 429. the engine has not been rebuilt, at least not recently. there has been some debate between my friends and i as to what octane fuel i should be using in it, so can somebody settle this for us?

It should say it in the manual you have, but for engines of those years you generally need to be running 91 octane or higher. However, I have been running 89 octane in my car and it runs perfectly fine.