I am not sure what amalgamation of parts would constitute a "stock 15" XR6" but your performance jives with what little I have been able to uncover about the newer STV hulls with small power. I have had my attorney looking in to what precious little precedent exists around overpowered boats and accidents. His analysis is that the factory rating of the powerhead assembly (based on the entirety of its parts) is the deciding factor. Given an LTVs 150hp USCG rating we think minimal liablity will attach to an XR6 powerhead assembly even if mounted on a SST/F1 midsection with a SSM. In light of the boat already being shoe boxed it should be very straight forward to rework the transom area to fit a 12" midsection. I am interested to hear from others that have run an LTV/STV with an SSM. Specifically for prop placement, what relationships between the pad, and 1)the propshaft centerline, and 2)the leading edge of the propeller hub did you find to be the best? What props ran best for you? We have located a cache consisting of a newer style mid with up and down, two SSM VI, one SSM IV, six new style four blades 10 X 15 1/2", 10.25 X 15 1/2", 10 X 16", 10.25 X 16", 10 X 17", 10.25 X 17", plus 16 and 17" three blades of unknown diameter. Current owner has never run the stuff but says the original owner bought it all for and ran it on a drag boat of some type.