My 4.3 is .030 over and 266.34 cu. in. which is 4.4L. The Gm race block is aluminum and comes with a 4'' bore and can be bored to 4.125" and 350 mains (p/n 10134371). Or there is P/n 10134351 that comes with 400 mains and has a bore of 4.177 with a max of 4.125. Both blocks can take a 4" stroke. Gm also has 18* heads that were used in the Nascar Busch series v6 along with intakes for the standard non-vortec heads and race heads.
Here is the review from motor trend.
http://motortrend.automotive.com/627...kup/index.html
Here is the link to GM performance parts catalog. Look on page 273. (Open with internet Explorer)
http://viewer.zmags.com/publication/...#/0ede9029/274