Hmmm....I would start with the easy stuff, like make sure the intake is not leaking any where. Check all the vacumn lines. Timing? Did you have the distributor out?
But, if the rockers are noisy I would suspect the problem could be here. I am assuming you have adjustable stud mount roller rockers, which will make some valve train noise but should not be making a tapping noise. How did you adjust them? You should be able to get them to zero lash by tightening the rocker as you rotate the pushrod, once you feel the resistance you should only have to tighten 1/2 to 1 turn. You should go through all of them making certain valves are in the proper location for adjustment.
Sounds like you also installed injectors and mass air meter. Are you certain the meter is calibrated for the 24 pounders? Or it could be a problem with the meter. Maybe to check it, put your old meter and 19 pounders back in and see if it runs better.
The oil in the intake is a common problem when removing the baffle in the cover. I installed a K&N breather and plugged the line from the filler neck.
Sounds to me you are on the right track as all the things I thought of you have already mentioned. Just need to weed them out one at a time.
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fordgasm
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