With Tracy's kind help, I stripped all but two discs from each rod
(making certain that we paired discs which would want to rotate in
opposite direction (hopefully stopping any - or most rotation).  Then
Tracy welded the discs, nuts and rod together. I inserted that
arrangement back into the 3" tubes, closed them up and flew the rest
of the flight with that arrangement.
 
The trip to Lakeland and home would seem to indicate I have found a
satisfactory (for now) solution.  I hit 6000 rpm static on take off
this morning and got up to 6600 rpm straight and level (which is 200
rpm more than I got with the straight (empty) 2" tubes.  I intend to
make one more modification by placing a cross feed tube between the
entrance to the two mufflers, the old "H" pipe hook up which according
to many sources, assists in lowering noise and improving power.