the split is dictated by the gears inside the transfer box
if you get different sized gears you can get whatever split you want, but it's going to be a bit pricey me thinks

you can also get the viscous coupling rating higher so you get more grunt to the front, i think the normal ones are only rated at something like 80 or 90 ft/lbs, i know the escos ones are higher but i can't get to the book just yet (its in the loft and we've lost the loft ladder pole thingy )