Re: 79 ranchero saved from the trees
If it is that heavily sludged, I would pull it apart and have it tanked. Re-assemble as needed (new parts/machining or not).
At the least, drop the pan and check the pump pickup. You may be able to clean it and then it will run like a champ, but as the sludge breaks loose in the engine and drops into the pan, you may experience heartbreak at a later date.
The above posted information is in my opinion only. It may contain copy and paste material(s). Your opinion(s) and mileage may vary.