The LS7 versions are easy to spot because they have a non functioning oil fill cap. You don't happen to travel towards Detroit for any reason do you? I'd like to pick a set up tomorrow.
I'll take any valve covers that don't have a baffle underneath. I would prefer the newest style LS3/LS7 just in case there are any differences.
The latest style will have the dowels that accommodate a fuel rail cover (dowels with bulbs on the end). An oil fill cap and bolts are preferred as well.