hey! sorry about the delayed response. i was outta town the last few days...
as far as the Mach 1 gauges go, the mileage "module" is the original from the car so yes, it is accurate. we wanted to make sure it worked before buttoning it all up and found out the car wouldn't even turn over with the Mach 1 module in there. I just thought the gauges were nicer.
it's late now but I'll send some more info to the e-mail you provided.