if you do plan on redoing the bottom end. might as well just get a B18 block and sleeve it and bore to 84mm, which is pretty much like a B20 in bore but with stronger sleeves.

If you plan on redoing the bottom end anyways, keep this in mind.
*stock B20 block ~ $800
*B18A block $250 + Sleeving w/ machining $880= $1130

For only about $300 more, you get stronger sleeves that the PRO cars and high HP cars use.