Hey sorry about the slow reply. Yes I built my J400 with the 914 rotax from new, I always like to be a little different. Major hurdles? not really any, probably the engine mount but even that went well. but as with any mod there is a string of further mods to carry out down the line, e.g. the constant speed prop is larger diameter so I had to extend the nose leg for ground clearance, and move the axles on the main legs 'up a hole',, it actually sits much nicer on the ground now. Take off performance is very impressive and at max TOW (700kg) we still climb out at 1000'/min. empty wt is 345kg About 15 kg heavier than a similar Jab powered aircraft, most of that is the 9 kg prop! Wt and balance were spot on with no need to add ballast. I have the radiator mounted to the side of the lower cowl and oil cooler just below prop in front, definitely no temp issues I can fly on 45' days with no worries! cruise is the same as Jab but with a slightly lower fuel burn. I am very happy with the conversion as it has proved to be reliable and low maintenance.