Originally Posted by Uncle Ben
I've been out of that loop for a short time but I believe the 203 reduction box is only a viable option with a GM transmission.
I first saw/heard about the conversion when Mark Whatley did Bruce Miller's 60 with stock t-case in 2000. Since then I have spoken with Jerry Nichols (he's done quite a few) and Mark about it and seen several that others have done the mod. IIRC, there is an adapter plate involved. But supposedly it is among the most economical ways to get lower gears with a stock "late" model cruiser drivetrain.
Like anything you add behind the tranny, it's really not suited for 40s unless they have longer wheelbase and/or serious suspension mods, it's mainly a wagon thing where you have more rear DS length to chop off to make room for the new box.