I ran this size on my 1000 + hp motor
water -10, -12 from pump to strainer. -12 from strainer to oil cooler then dump -10 from strainer to block -10 from block to dump
oil -12 for everything, remote bypass filter.oil cooler
fuel -8 for everything even vents, - 6 for return lines =2
-20 for a ballance hose that goes to both tanks at the rear bottom of tanks to keep em both equiel sp. Thanks TJ for the idea