Mine was a B8 with a bar axle and rotax 532
there was a conversion kit supplied by Gary Layzell to convert a stock bensen to centreline thrust (droped keel conversion)
basically
cut the keel a bit before the prop (to allow for a lower prop)
add suspension and do away with the axle. (thus raising the whole gyro slightly otherwise the gyro will not rock back on it's tail properly)
mount the gearbox upside down (reducing the prop centreline) hence the need to drop the keel a few inches
bolt the new keel and tail section back on under the original keel
raise the seat, make sure you can reach the pedals, (may also need a longer stick)
there were a few other bits, best communicate with Gary as he did a few I think.
I guess you are starting with a stock bensen (if there is such a thing)
best to ask Gary about it ... but he is not easy to contact , He is now residing in the south of France. but may be able to offer advice if needed.