well that looks like water, I did not use assembly lube when I did my top end overhaul, what I did was just squirt Mobil 1 from my oil can on the cam lobes, lifters, pushrods, etc. Then before starting, I grounded the high tension lead of the coil and cranked it till I saw oil pressure on the gauge. Then started it up and that was the vid I posted above.
you could take a sample of this, put it in a glass jar like a Mason jar, and let it sit. see if a layer of water appears on the bottom. if not maybe it is assembly lube but it would be good to know.
what led to the failure of the old engine?
when I did mine it was a gamble, I actually had salt water in the oil, changed it 4 times, pickled the engine well, then took it apart, rolled the dice and put a set of reman heads on it. Turned out OK but was a gamble, for sure.