cooleto - i'd go with the FX with a 13 x 6 and not go through the potential trauma of dealing with the TH75. i'm not saying it's a bad engine, but it does have more quality issues than the O.S. line of FX engines.

14 x 8 is fine for the 91. I was running a master 14 x 6 and seemed as if it had some power to spare. Mine was not pumped.