Hi,
I got a Sierra 7'' diff but the front flange looks not familiar to me.

I need to build my propshaft but I do not know what kind of CV flange I need and where to source it.

The diff flange have 8 holes, but 4 holes have different PCD. Any help ? thanks.

The propshaft bolts to the (4) tapped holes in the input flange of the differential (M10x1 thread I think).

Best to go to someone like Bailey-Morris or Dunning & Fairbanks and they can make up a prop-shaft with any flanges/joints to suit your installation.