Some of the later vortec blocks are missing 2 bolt holes for the timing chain cover, it's not a huge deal and they can be drilled and tapped if desired but as long as you rtv both sides of the gasket and make sure all the other bolts are tight, then you really don't need the missing 2 holes.

Good video. Can i go the other way around and put a vortec cover on a older bottom end? I need the crankshaft position sensor. I'm wanting to run a older block with vortec heads in a 98 silverado and keep the vortec injection.