I have a Tiger II with a 55 AX on it. It flies sweet. That is the only Tiger that I have built to date that did not take any nose weight. The extra weight of the engine is usable weight instead of dead weight. All that said I did not have a 60 size engine mount that would fit between the cheeks of the Tiger II. There is one out there some where I am sure, but I did not have one at the time. That is the only reason it has a 55 on it. It has the same foot print as a 46. A FX 91 has tha same foot print as a FX 61. I have a Tiger 60 with one of those on it. It also flies great. I like the extra power.