This mainshaft will not work with OEM 1st or 2nd gears.
The first gear ratio is 2.3125 and the second gear ratio is 1.65. It is rated for up to 500 horsepower.
This is the mainshaft from the Gear-X Drag Kit, Pro Spec I, Pro Spec II and Pro Spec III gear sets.
The picture is shown with the first and second gears for the countershaft side but they are not included.