First of all is this a 5 liter Ford, or Chevrolet they are totally different animals. The older Chevrolets have an adjustable valve train that has to be set right or the valves won't open far enough or close completely either way it will cause problems. There is a 2 step procedure in the shop manual that tells you how to set the engine for the first half of the adjustment where you adjust certain valves then you turn the engine as specified then adjust the rest of the valves. This in Merc, OMC and GM shop manuals. Usually you loosen the rocker arm nut till you can move the pushrod up and down, then tighten till that lash just disappears, then one more turn (but some say a half turn, some say 3/4 turn), GM who made the engines says 1 turn. And others say to use an 8 stop procedure feeling its more accurate. I used the 2 stop method in the shop manual when I installed my new heads and it started right up and ran fine.
