[Will]

you could build a 400 to perform similarly to an LS but there are some factors working against you.

Mainly intake and engine management. We simply don't have the FI specific intake manifolds and engine management systems available to us.

I think the closest you could come would look something like a basic forged rod, high silicon content forged piston at 0 or even +.005" deck, modern ring package, topped with a set of KRE or Edelbrock D-port heads with some port work to get into the 290cfm range and set to ~10.5:1 compression. Run a moderate roller cam, somewhere in the 218-224 @ .050" range on the intake with a relatively wide LSA and use whatever exhaust duration works to get the overlap and flow balance you need. Run some Harland Sharp 1.7 ratio rockers. Intake will have to be chosen from what's available and a stock or Perf. RPM would probably be best though maybe a Torker II or HSD/Northwind intake would work okay but the runners are really too short on those for optimum low end/midrange performance (this is where the intake issue comes in) topped with a throttle body FI system like a Fitech that also controls timing.

Sure, you could get more in-depth with a port injection system but I'm not sure how much better that would actually be and a proper intake is STILL an issue.

Seems to me a 400 set up as above ought to perform on par with a typical junkyard 6.0 LS. Might not be as efficient/get as good of mileage but the power should be there.

Power and efficiency are in the heads and intake and that is where it's hard for the Pontiac to compete.

Not talking about cost, just answering the question originally posed.