Seating or aligning the thrust bearing. Loosen number 3 main cap till bolts are just snug, pry cap rearward with a pry bar or lg screwdriver, then push crank with a mallet or prybar forward from any other main bearing. Idea being to push crank the cap forward enough to line up with the block half of the bearing providing a even surface of thrust bearing for the crank to act against being pushed forward from auto trans pressure on the T.C. or a pressure plate on a manual trans, depressing the clutch pedal.
Looks very nice BTW.
I'll have remember that when I build an engine!