I agree with going with a B18 engine, as there are more parts floating around, more options, as of right now, the tranny for a k20a2 sucks, 2nd and 4th gears have problems when boosting over 260HP. They're just not able to handle that much HP, guy who blew 3 tranny's had 290whp so he had 310+hp.
I think the B18 is a really good engine, but the K-series engines are were it's gonna be at, it's just gonna take time for them to build up more aftermarket parts. People do it, but it costs so much more then dropping a B18 into your Civic and putting a turbo, I think the price would be less then a turbo setup on a k20a2(parts, labor +tuning)
that's my 2 cents.........don't hate, haha