Probably too late but an OS AX 55 with about a 13x5 or 13x6 prop hauls the 40 around with authority.
You can get into trouble with this engine particularly on a full power go around starting with a high angle
of attack; it can and will tip stall under the right conditions. The tail dragger is more difficult to taxi and
there is a learning curve to go thru. The ultra stick 40 is a nice airplane and it can be converted to a
tri-cycle gear fairly easily. To get to desired low weight I used a Dave Brown engine mount as H9's is
really heavy and Hitec HS 85 MG servos. Skip the flaps and save more weight. A Macs muffler boosts
the power ( thrust ) and saves more weight.