First thing to realize is that as long as you have some gap the motor will start & run. On a number of occasions i have set valves on a 617 by feel; no feeler gauge. It will have a rattle if they are too loose.
Your problem doesnt sound like valves. The OHM test for GP's is about as useless as an eye test while wearing sun glasses. It will tell you if they are definitely bad, but not if they are good. Pull the GP's & test them properly by watching them heat up. Its the ONLY way to test to see if they are good. If you reconect them while they are out & turn the ignition on you can see if the GP relay etc is good.
You may have disconnected something on the IP when you took the valve cover off.
Good Luck.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving