the blocks are infact the same...the b20 has a factory sleeve job, and is bored out to 84mm. However, those sleeves are weak still.
If you want to beat Lt-1's (I dunno about Z06's) you could do it with a GsR, bolt ons, LSD and some suspension work. I start out trying to beat 5.0's first, then work your way to LT-1's, then Z06's and vipers.