Specifically, the E-Rod they are using is the L33, available from these vehicles:
2005 to 2007 Chevrolet Silverado 1500 4WD
2005 to 2007 GMC Sierra 1500 4WD
E-Rod is sold by GM Performance
Here is their site:
http://www.chevroletperformance.com/...ction=overview
The E-Rod package includes pretty much everything to get the engine running.
They also have a very appealing (but way expensive) LS3 6.2L option. It's the same physical size as the 5.3... but I believe cost is the reason nobody goes bigger than 5.3.
I've done a LOT of research into LS engine choices and have come to the conclusion that when it comes to cost vs. hp, the Generation 3 5.3L is the most practical and economically friendly choice. Also, all Gen. 3 and 4 LS engines should pass emissions requirements regarding year of engine manufacture, since the LS1 (Gen. 3) came out in '97.
Let me know if you have more questions on this... I've learned a lot in the last 9 months that I've been searching and would love to share.
(PM me...)