im using a 4-2-1 oem manifold off of a 98 civic ex with the cast upper 4-2 part. it alows you to use the oem 5 wire and read all 4 cylinders right after the head ports and make the most low to mid range torque.
as for the 4.08 final drive out of the lx civic 4 door. i used this for the build because of the toques multiplication of the shoeter gearing and the rpm range that the hx likes to use lean burn is 2200 rpm up to 3200 rpm. this gearing puts me in the ideal rpm range in 5th gear at 60 to 70 mph. 60 mph =2400rpm and 70 mph= 2900rpm. this also drops the lode on the engine and i can get lean burn in all gears but 1st.