Is an 85mph speedo a direct swap for a 100mph or will it give me inaccurate readings? I've got the 100 in my 77 4wd and an 85 in my 80 2wd. The 2wd has the tach and I would like to swap the entire cluster because of different fonts and colors. Will I have to run a separate wire for the tach hookup at the distributor? Does the fuel guage work without rewiring? What about the speedometer gears in the T/C? Can they be swapped to make everything work OK?