What an idiot, here is a little tid-bit of info:
According to THIS
speed/RPM calculator assuming you have a .75 4th/5th gear ratio, with 25" tires (12.5" radius), at 8300RPM you would need 7.16 rear axle ratio . . . I assume you don't.
Tell that guy to stop pullin your leg and not be a smartass tryin to make some money and problems.
RPS' Gear Ratio Chart - LINK
You can use math to prove he's an *******!
(don't flame me if I'm wrong, just tryin to help)