Help! Swapped 302 heads on my 318.

Ok, lets back up a little........what heads did you take off? What is the lift of the cam? You stated it is a solid, tell us more. Do you have the adjusters set correctly? Are the push rods seated into the lifters correctly? Were/are the retainers running into the valve guides? Are you coil binding the springs? There are lots of things it could be, observation will tell you what is wrong.