What kind of a rebuild do you want to do? Aftermarket rods/pistons? You don't want to bore out the block unless you get aftermarket cylinder sleeves, which is highly expensive for what you want to do and overkill. You won't need more than the 2 liters the B20 would give you. If you want higher compression, you're going to need to get aftermarket rods and pistons. I would use something like a Hondata S200 to tune the car with, and have someone experienced tune it. That setup along with a GSR tranny should probably get you near a 14 flat...it's a setup I've wanted to build for a while, never seen anyone with it before...so I can't give you any exact numbers. You can use your LS clutch with the GSR tranny, but I'd get an aftermarket clutch while you're in there replacing the flywheel.