***UPDATE****
thx in advance for any advice/feedback on my issue
These are the steps I followed in the order I followed them...
1) Engine intact nothing removed/apart
2) Pressure tested cooling system, held 16lbs for over an hour
3) With cooling system under pressure I cranked the motor ( coil unplugged) looking to see if the pressure gauge bounced/moved. Nothing changed. I had assumed if a head gasket issue, this might show up on the coolant gauge.
4) with cooling system under pressure, removed spark plugs, watching gauge each time, so see if pressure bleed off. nothing changed.
5) Plugs all good, light tan/brown on tips
6) Removed oil filter, keeping contents in the filter until out from under the car. Then poured contents in bucket looking for coolant, foam, film, sludge....but nothing.
While the above I believe is all good, its no closer to telling me whats contaminated the cooling system.
I believe Im down too...
1) Cooling system was contaminated from
a)new rad
b) uncleaned coolant passages after rebuild
c) orignal heater core had contamination ( had not been cycled for 20+ years and wasn't cleaned out prior to engine install)
4) resto shop mixing two different coolants
5) someone playing a prank
6) crack in block only weeping oil into coolant when engine running / under oil pressure
7) other
Next steps...
1) Run motor tomorrow, one more time with water flushing out system AGAIN
2) Drain again
3) add Blue Devil Coolant Flush , add water, run motor 10 minutes
4) drain
5) refill with water, go for a drive
6) pray to the motor gods