I just did an engine swap on my ranger. what happened is I got a 5.0 from a 91 bronco, put 87 mustang heads on it, now my pushrods are too short. so I got some longer ones and the engine runs, but i think they are too long cuz I have just about no power. but it is idoling and revs up. the engine block is hydraulic flat tappet but the heads are from an 87 mustang that had roller tappets. how different is the cylinder heads between 91 bronco and 87 mustang.