The pump is aftermarket. I will upgrade the lines from the pump to the bulkhead from 3/4" to a larger diameter. The main coolant lines are 1 1/8" ID.I would check the other items mentioned before swapping out lines. Also, systems normally have return lines wider diameter to lower pressure and increase flow. Stock LS pump is normally 1/2 and 3/4" diameter lines, which is normally sufficient for flow differential. The newer LS models have additional steam ports that are not fully drilled out....you may have one on prop side of engine that would be highest point of water jacket for better burping....but not likely needed if you can evac all the air and make sure the pump bypass port is blocked or fluid won't circulate thru radiator.
I will rely on the expertise of Hutter Performance, as they will perform this procedure.Funny thing about that 'mud' link is that the OP had it right, and almost everyone else in that thread...didn't.
TX, once you get the steam ports added to the heads, how are you planning on routing the vapor lines to the swirl pot? They need to be mostly 'up hill' to the pot, and the end in the pot needs to be always submerged in coolant, so that the engine can only draw liquid back from the pot as it cools.