Carl,
I have 338 gears in it.
I wouldn't recommend taller tires with those gears. If you are running a three or 4 speed with a final drive of 1 to 1, you are likely suffering from heavy lugging on the onset of every shift, followed by the need to make the engine scream before the next upshift.
Not exactly conducive to decent gas mileage. Have you considered a T-5 with overdrive? If you do, you will need to go with 3.73 or higher ratio rear gears. That setup will result in the engine remaining in the optimal RPM range for a stovebolt engine upon every shift and you won't need to make the engine scream before each upshift. That will improve your MPG.
