that looks like a mk4 to me. Gen 5 and 6 don't have fuel pump pads. Gen 5/6 have one peice rear mains. The timing covers will not interchange, oil pans are different and you can run gen5/6 heads on a mk4 block with the right head gaskets, but you can't run gen 5/6 on a mark 4 block.
Based on the lack of an oil galley plug at the left pan rail, the presence of a fuel pump pad, the shape of the casting around the cam bore that is required for the "priority main" oiling system and the sculpted area between timing cover rail and fuel pump, it's a Gen6. More/better pics could confirm.