I've read the problem is due to the return oil from the cooler is what supplies lubrication to the O/D section & so the volume is needed...I've done two 518 conversions & had Fine Lines bend me up cooler lines to stock shape out of 3/8 tubing, modified the stock radiator mounted cooler by drilling out the fittings while blowing air into the cooler from the opposite fitting & modifying every fitting in the flow path by drilling it to the ID of the 3/8 tubing...Neither vehicle has had any problems so apparently I haven't compromised their needed flow to badly...