I really don't think it made 1160 with bb2's and it sure didn't at 7900 rpm's
And to boot I don't think you can get close to what the bb2's made with iron heads. I'm not sure, but some of the other guys can help with the iron heads question.
If it did make it at 7,900 why so high? If it's in a 4,200lb mud truck your probably running low side and shifting so you need to peak lower than 7,900 so it will turn back up after you shift.