Flutter below 2k rpm

I just swapped in a 2.76 pig for a road trip to Sun Valley to watch Supercars run flat out.

As far as compression ... I have a stock 5.9 short block that I refreshed with new bearings / rings / linehone / square decked block etc. .028 head gasket for good Squish
The heads are (IMM) Brians EQ magnums with 2.02s / 1.6s , cut guides , springs and his valve job . Supposed to flow 270ish @ .550