a friend of mine bought a 1990 with a 5.0 in about a year ago. we recently decided to rebuild engine. when we pulled the engine i noticed that the back of the head(the part near the firewall) had a sprakplug busted off in the head. there was one on each side. i dont know what it is but it looks like someone was trying to plug the holes in the back of the head. is it for emissions or somthing? should i just leave them open?