Hey, nice to see you made it here, I'll post my same reply i did on the other forum and we'll see if it strikes up some conversation,

The trail blazers actually come with the 5.3L option. The 5.3L bolts right to a 4L60E (like in the silverados), and the 4L60E bolts right to your IL6. The 4L60E also comes in the fbody's and bolts to the LS1, the 5.3L and LS1 have the same bolt pattern and mounting bosses. So, yes the LS1 will bolt into your trailblazer.
You'll need to get a harness from a 5.3L trailblazer also. The engine mounts will also be needed.
You can use the LS1 longblock (engine,internals,heads) and use the 5.3L intake, valvecovers, coils, oil pan, manifolds, etc. everything that comes with the 5.3L. So, when you pop your hood, you can tell everyone it's a 5.3L
The 5.3L and LS1 engine parts are also interchangeable.

I say do the swap, I've done several 4.8,5.3 --> LS1 swaps and it's an awesome upgrade.
You can get an ls1 longblock for about 1200-2000$ depending on miles.
The truck accessories are also easy to get, intakes are about 100$, coils and valvcovers are cheap, and the oil pan would be another 100$. Not a bad upgrade for the cost.
You can find more info over at ls1truck.com i'm not sure if anyone over there has done the swap, so it would be interesting to chat about.

later,

allen