remember the b motors are na engines that are designed for high revs and lightweight. they have an open deck block so i would sleave it if your going to do any machine work. if you really want to increase displacement i would increase the stroke instead of boring it out for a honda turbo motor. easiest and cheapest way to increase stroke is by going with a b18 block with forged internals.

what hp you get form 12lbs is dependent on the size turbo you are looking to get. you can have a t2small putting out around 230 at 12 lbs or a t3/t4 putting out over 400hp at 12 lbs. so i would do a bit of research on this to see what you want. try www.honda-tech.com they have oodles of info on turbo hondas.

if it were me and i wanted a turbo car i would start with a car with a factory turbo like a dsm or an sentra with a bluebird swap, instead of trying to build one from one of the best designed na engines out there. but thats just me. good luck man.