8. After bolting the driver side injector manifold to the head, it was time to address the coolant lines. Unlike a traditional intake manifold, the Hilborn design does not have provisions for internal coolant passages. Jeff’s solution was fabbing up a custom distribution log from 5/8 inch stainless tubing that’s fed by two 1/2-inch hard lines attached to the rear coolant outlets on each cylinder head. From there, another 1/2-inch tube directs coolant from the log up to the thermostat housing. A second line sends coolant from the log to the heater core.