I saw someone selling hooker shorties here....how much HP would I gain with a cutout (instead of the LM I bought) and a whisper lid with these headers?

They include ypipe

 

With the y-pipe you might gain as many as 10 or as few as 5. The stock manifolds already flow really well, the shorties aren't that much of an improvement over stock. Most of the gains are going to come from the y-pipe, that stock crushed one is just plain junk.

 

shorties are a waste of time and money.

 

Yeah basically. I was just saying it nicer.