I recommend you read Jerami's Super FAQ above. It will help a lot.
Some of the info you requested:
LS1 is a 5.7 Liter (346 cu. in.) V8 that was used in Corvettes 1997-2004, Camaros 1998-2002, and Firebirds 1998-2002. Horsepower ratings from 305-345. Bore 3.900 x Stroke 3.622
LS2 is a 6.0 Liter (364 cu. in.) V8 being used in 2005 Corvettes, SSRs, GTOs, and I believe a Cadillac. Horsepower 400. Bore 4.000 x Stroke 3.622
LS6 is a 5.7 Liter (346 cu. in.) V8 derivative of the LS1 that was offered in ZO6 Corvettes 2001-2004. It's horsepower 390-405. Same bore stroke as LS1
a 408 is a LS1/6 that has an increased stroke to raise displacement to 408 Cu. In. 4.030 Bore x 4.000 Stroke