Engine date I recon is 25th May 1965 (650525 part of engine number).
Why do you think the coil needs replacing? No spark could be as simple as corrosion on the points, easily cleaned with sand paper. I have used Briggs Bits in the past for engine spares.
The Hayterette was launched in 1957 and continued in production, with various changes, for 62 years. I have a very early 2 stroke one.