smacking the crank back and forth with the bolts tight seems odd to me?
what you're trying to achieve is even contact on top and bottom half of the thrust bearing when the crank is pushed forward by the converter and or clutch. depending.
you don't want to have say the top half of the bearing to touch the crank and the bottom still be off it a thousandth. that would put more load on a smaller section. nothing forces the crank backwards while running, so that's less of a concern.
my experience is this all matter way more in other engines.. the ls isn't know for thrust issues, up until you go drag racing with crazy high stall speeds, but by then you'll have a tranny builder on speed dial haha.
the last one I did, I did the finger tight, pry the crank forward and snug the bolts so the bearing shells don't move. after tq is complete, check your total end play by prying it front and back. as along as that's in spec, shouldn't be a issue.