oldmercs.com has serial number listings. It seems to be a 1961.
The water pump is dirt simple to replace, although I was given the tip of turning the motor on its head when you put the LU back on. And for sure, have it in forward. It is nothing like the earlier models for water pump replacement. No special tools needed.
I have S/N 1412843. Sweet running motor.
Taking nothing away from other suppliers, Ferguson-Poole gets my vote for parts. I have bought many from them.
It takes a special small fuel connector. If you didn’t get a tank with it, you will have to buy the fitting. They are still available new from F-P.