I think one of the best mods right now would be:

Real Cams
Stroker/overbore kit

Both of those can be interchanged between the N/A and SC motors, both can be used in about 100,000 cars, and both are substantial power adders.

If you are realistically looking to add serious power, cooling mods might not really get you there. With the HEs out there is already some decent progress, add Code 3's new Intercooler design, a modified thermo, intercooler pump, and some spacers and you are pretty good.

But like I said we'll do what the community wants as it's just more fun that way.

I have an engineer that can sketch us up cams, cranks, and pistons. He just mocked up a V16 engine based off of 2 LS1s. It's just a CAD but pretty cool.