Can a 400BBM w/cheap aluminum heads compete/dominate against the street LS?

^ yep.
also, that article that IQ52 posted had some builds that were 400ci, making alot of power too. No details but goes to show you can make some power without the stroker crank. get the heads done right and find a piston that will give you decent compression...

They also did a low compression 400 build that was quite impressive.