Cutting Prop Shaft - Flex Coupler

Hi Everyone, Still trying to solve my flex coupler problem. I don't like the idea of buying the original farrymann part (over $500) then eventually replacing the engine. I would like to go with a product like this: http://www.thermoboat.com/ptmarine.htm or the aquamarine product, both said to reduce engine vibration/noise. Unfortunately, they are both much longer than the original coupler, so I would have to cut the prop shaft. Does anyone have experience with this project, or with either of the above products? Cutting hardened steel seems very difficult, and I don't want to go through the pain of doing that to find out that the products don't work! Matt