The heads pictured above have a huge base on the bottom of the casting, these are definitely a brand new design. They also have to be production heads (very close to them), it is required in GT2 to run the stock castings I believe but the water passages can be altered for cooling and such (individual cylinder cooling). This thing was based off the 7.0 so the block should look very similar.
I heard that the direct injectors are below the intake ports and they face the pistons The the valves are 2.18" x 1.60" that makes the valve area (per displacement) greater than the LT5. Maybe shallower valve angles or splayed valves to round up the "new combustion system" GM was talking about.
Some info here:
at a minimum they layed over valve angles - possibly 11*. it looks like straight lsx-dr tech. the exhaust face is almost in line with the bolt heads, and the intake face is vertical instead of 5*. that may account for the wider valve covers - and not splayed valves. they probably need the room that inline valves gives for the injectors.
the 5.5 and 5.0 share the same 81 mm stroke. gm racing used a 5.0L in the g6 race car. if the deck is unchanged from the gen iv, then it must be using super long rods. imo gm will want to keep a moderate rod/stroke ratio. this makes me suspect that the bore and stroke are race only, and that the production engines will have more square dimensions. they should be awesome regardless