Re: electric start on 1979 johnson 25 hp
Get in touch with the BEST outboard mechanic in your area. That will work out the best & cheapest way. You / the mechanic WILL PROBABLY NEED TO use shims to get a good gear mesh. I put .030" of shims under mine. Perfect. No jammed starter gears into the flywheel teeth.
Edit........Check the mesh gap EVERY 45 degrees of rotation. They are not all perfect.