That sounds about right as far as cost but I would call CDI electronics and confirm all you need to do the conversion. Depending on what your willing
Pull lower unit and see if exhaust tube blocked with carbon....
You will still get a solid pulse through the pulse limiter and can use it. The only time it comes into play is if the motor backfires on that cylinder.
That motor will run fine on 100:1. The problem came about when you stored the motor and didn't fog it out. Then they would rust up inside and freeze up.
If by "top of the risers" you mean the elbows, then 86 degrees at cruise is a very good temperature. These are cooled by raw water so it would