early 2000 motors had 853 heads, late 2000 had 241 heads. The 2000 was the first year for the revised block that allowed for better oil return so you dont spin bearings. has LS1 intake and a bigger cam than 2001 up motors.
2002 motor has better redesigned rod bolts 241 heads and the LS6 intake. has a smaller cam (not much smaller) also has the good oil return. it dosent matter if its an LS6 block. the LS6 block is actualy weaker and the LS1 block is more desirable. if there is a price diffrence. i would buy the cheaper one. you are going to want to replace the rod bolts reguardless. and a brand spanking new LS6 intake to your door is like $400, but if you are going to cam it or put heads on it you will want a single plane carbed intake with injectors and a huge TB anyways.