Hi Gary.
I also have a 55hp Tohatsu that I could not find the impeller for. My model is the M55B and the impeller part number is 353-65021-0. This is discontinued but I managed to find two on a shelf in a boat shop here in Western Australia. I had to fit one of them in my motor but I have to other impeller here in my hands. Evidently, it also fits the 60 and 70 models. Anyway, I do a lot of urethane casting so I am going to cast a load of them up for myself and to on-sell so people can keep their motors running. I want to try to buy up a load of rare impellers and cast as many as I can as I can’t see the point of throwing out a perfectly good motor just because it needs a new impeller. I also have a new impeller case on the way which I will also cast in urethane. As the properties of urethane can be varied, I can make materials with different hardness and it also acts as a natural lubricant. That’s why it’s used in car axles as bushes. I can also repair damaged impellers as long as it has a few fins and the key way. Repairing impellers with cracks is pretty easy.
Anyway, drop me a line if you need any help with yours.
Scott.