I have a block with GM in the lifter valley and on the main caps, the 1255506 casting number on the bell flange, and 506 on the back of the block, but no Navistar diamond and no 506 in dots in the valley. For those who see a lot of chinese/AMG blocks, what do I most likely have?

It's crack-free, looks beefier with the thicker taller main bearing caps etc., just want to be sure before I pour a lot of money into a buildup . . . .