The reason for the b18c's smaller combustion chamber is for a higher CR, I wouldn't worry about the trade-off of have a b16 head vs. a gsr head, the results won't be noticeable compared with the amount of difference given by switching to a gsr block. Just go with a b18c block. Since you drive a 91 integra (just like me btw) no exhausts except for 90-93 exhausts will fit, unless you decide to go with a custom setup. I don't think skunk2 makes an exhaust for our year integra, but greddy does, and so does thermal research and development, which I've heard good things about, as long as you don't mind a loud exhaust, which I am told they are. Anyway, if you just want to make up for torque, and don't live in CALI, get a turbo, it's probably cheaper, it's adjustable to your driving habits, and you don't have to worry about another swap. You'll get the torque you want, not to mention you'll be able to keep the b16 with its ideal engine geometry intact. Just my 2 cents.