Sounds like you have a cam lobe that has gone flat. If the rocker doesn't open and close the same amount (disconnect the coil before you crank) as the others, the cam lobe is flat. This is common on hydraulic flat tappet cams that have some miles on them, or weren't broke in correctly. Did the motor register oil pressure when you ran the engine? If so, You can take the ultra cheap approach and change out the cam, it will probably run okay. This isn't what I would do, and many will disagree with me, but you stated you didn't want to pull the engine. However at a minimum, I would slap the valve covers back on, drain the existing oil, change the filter, add new parts house (O'Reilly's, Autozone, etc.) 10W-30 and Sea Foam to the engine and run for 20 minutes, prior to pulling the camshaft and replacing. This will flush out the motor of existing material from the cam failure, but it won't undue existing damage. The cam shaft change with the motor in the car isn't overly difficult, just time consuming, and you can find a fox body cam change (in-car) all day long on UTube. Let us know what you decide and you can get cam change recommendations for your existing combo.