Leave one wheel on the ground, then rotate the other wheel TWO full turns while you count. This will give you an accurate number. If you lift both wheels, the wheel you can't see will turn a little (or a lot) in the other direction and screw up the count. If you have one wheel down and rotate once, you need to double the number to get your ratio.
I believe 3725899 is an old Chevy car rear end with the drop-out center section. That type of rear end was used from '55-'64, with different widths & spring mounting hardware for different cars.
Google 8725899 rear and there's an old ebay listing with pics. Casting numbers are often mistaken, especially if they're old, rusty, dirty, etc.
Last edited by jimfulco; 08-25-2006 at 11:26 PM.