I don't remember the exact weight differential, but I believe it was somewhere around 80-100lbs. The fact that an H series engine would sit further to the front of the engine bay relative to a B series coumpounds the weight problem. Since it's further away from the car's center of gravity, it has a longer lever arm and excert more downward force than it would if it were closer to the firewall. You can make an H series swap into a Civic relatively streetable, but it'll take a good amount of suspension tuning. Most notably higher rear spring rates, and a larger rear swaybar to counteract the understeer induced by the added weight up front. You would have to get your suspension settings right, or else the handling characteristics of the car will be compromised.