Flushing out old oil
Getting back to what you said
I would first flush the engine with Wynn's engine flush !
i.e. pour it in & drive it for about a 100 miles without Reving the engine too high. Why not pour in WM Penn valve ease into the tank, whilst you're at it.
I am not a fan of additives, but these products have prooven themselves to me over 20 years.
Then you properly flush your oil when hot & pour in a oil formulated for old engines, such as Caltex Delo Gold 15W40.
I am not advocating the use of these liquids, but that's what we can get here :bigpimp:
If you now remove the tappet cover, you should see little sludge remaining

If it is sludge that held the motor together, then you can expect a spun bearing in the near future

I have already removed 40 year old tar from a motor with Voco or Petrolium, but that should hardly be neccesary in a engine that runs :thumbup: