I think that the factory stopped using them after a certain time. You are correct, it goes behind the timing cover, between the crank timing chain gear and is held in place by the harmonic balancer. It is supposed to throw oil off the gear, away from the front main. Honestly, you are probably just fine without it. Sweet looking engine BTW. Sure looks like not enough clearance between the pushrods and their holes in the heads....have you checked them for clearance through the pushrods range of motion as the valves open and close?