I'm back on it. I'm now re-setting the lifter pre-load, and the T&D instructions, combined with Barry's, were to turn the adjusting screw in one turn, then measure the length for the pushrods, and order them that length. Then with pushrods in place turn down one turn to engage the pushrods, and then two more turns after that.
With the engine at TDC I just backed off #1 rockers and what I found probably confirms Howie's suspicions. Fully backed out the pushrod turns freely but has no up/down movement. I can turn the adjustment screw in 1/8 of a turn and the pushrod now won't rotate. Turn the adjustment screw in 1/4 turn and the rocker starts to go down, at 1/2 turn the valve is dropping.
The original adjustment was 3 full turns down. I am stumped, I assume the lifters are now filled with oil and are providing significant pressure on the rockers. My question - the T&D instructions are below - should the rocker move at all when I'm setting the pre-load? How much pre-load should I use given that at 1/4 turn the rocker is starting to tip?
Video of the rockers moving after 1/4 turn
https://youtu.be/zqeiVXvb2AMT&D Instructions
3. DETERMINE CORRECT PUSHROD LENGTH
Place a pushrod length checker into a lifter and install a rocker arm assembly. Be
sure the cam is rotated to the base circle. Seat the bottom of the adjuster screw up
against the recess in the rocker arm and turn the adjuster screw clockwise one full
turn down. This is the initial adjuster position. Adjust the pushrod length tool to the
proper length, remove from the engine, and measure its overall length.
The rocker arm should not be operated with the adjuster screw more than one turn
up or down, from the initial adjuster position. Doing so can cut off the flow of oil to
the rocker arm.
4. FINAL ASSEMBLY
After all of the stand heights have been set; check the head bolt torque to be sure it
is set to factory specifications. Put the rocker stand back on and place a rocker
and shaft back on the stand to assure good rocker to valve alignment and
torque the stand attaching bolts to 55/65 ft-lbs. When the stands are aligned and
tightened down, place the rocker arm and shaft assemblies on the stands and
tighten the shaft hold down nuts to 25 ft-lbs. After all of the rockers have been
tightened down, set valve lash and torque the adjuster screw jam nut to 5/20 ft-lbs.
BTW does anyone know what 5/20 ft-lbs means (last part of the T&D instructions)?