I believe I read this from JetManiac too, but the stock SJ mounts were really meant for the 650 61x lower horsepower motor design. They were used on the 701 6xx as well because no sense in changing them up adding expense to the machine when these "will just do". The original SJ mounts, as mentioned, meant for the 650 61x were not meant to handle the higher horsepower of the 701, and to further that the at the time newly redesigned 701 62t with higher airflow and hp rating. So they succumb to being more jello-like pliable and soft rather than a solid connection to the hull, they just aren't good enough to live for long under the higher horsepower requirements. The bigger, beefier couch mounts were actually intended to be used with all runabout models from 701 through to 1100 so Yamaha only had to produce one style of mount flange which is the same one the SJ uses, just a larger urethane pour mould which is super simple to make, and save on new moulds and casting practices for a broader range of flange plates, bolt spacings etc. Yamaha likes to keep production costs low and simple, so, use what you have for as long as possible and in as many applications as possible. It works for us too, we get the benefit of having a huge parts supply that is almost fully universally usable
