Regardless of engine type, or brand of gears used, a Dana 30's ring gear is the same diameter.
Any difference in size would be reflected in the size of the teeth on the gear, not the diameter. Lower gears = more, smaller teeth.
That's why "low gears" (high numerically) are more fragile than "higher" gears.
Now you may need a different carrier as mentioned, depending upon what gears you presently have, but again - Gear fittment should not be an issue with the D30 housing.