Ok this is the update and probably my final post unless something goes awry. All the prep appears to have paid off IMHO. Fish were stocked last Saturday. Was adding Prime/ Safe because at time ammonia was in .08+ range. Changed water Monday (50%). Added some stability and Fritz. Ammonia now approaching zero. Tested Nitrates. 0. Tested Nitrates, 20. Nothing has been added to water since Monday.
Will change water tomorrow. So appears tank is cycled (I know there is still BB growing/balancing but it appears to be tracking very well).
All this with a VERY high bioload.
So I have avoided the water change/ adding shelf BB + worrying drill.