Thanks SerpentRoyal, and Zap.
So 3" all together. Hmm.... Not so good.
It seems that the 1U rack Mount 775 HSF comes in two flavors.
With Fan Made by Dynatron.
Passive all Copper, made by Spire.
Assuming that there is General Good airflow in the case.
Would the quiet Spire be good enough?
TIA.