Yep looks like its a gen II vortec. Not an ls vortec. GenII and genIII blocks look very different. Its very easy to spot an LS block once you seen a few pictures of one.
Here is a link to what gm sells. I would look at the fast burn or vortec heads both will make north of 400 hp with good cam. The vortec heads would be the better choice for efi. Sky is the limit for carb. I like 18 degree stuff but its a ton of money to swap it all over.
Your stock heads are going to fizzle out at 300 or so hp. You will want to use a cam that matches up to that a little better.
Hope this helps.