dont think B series box fits into a prelude chassis, the amount of work that would be required, custom link, mounts. The set up doesnt exist for a reason.
he's problem is the turbo is way too small for the motor, turbo honda's like big rear housings.
he's gears isn't the problem either, longer gears is suppose to be better for turbo, and even if he wanted shorter gears, a mFactory 4.6 FD would be better option than your opinion.