Still working on this, and there must be something I am missing.

This is a 1987 Mercruiser Stern Drive with a 3.8 Litre 165 Horsepower four
cylinder

I have replaced...

Spark Plug Wires
Spark Plugs, gapped to specs
Distributor Cap
Rotor
Condenser
Ignition Points, gapped to specs
Coil

I have checked and rechecked to confirm the parts are correct for the
application

I have drained gas tank completely and added 10 gallons of fresh gas
I have tried with starting fluid
I have looked down the carb to verify that it is getting fuel
I have verified that the in-line circuit breaker is not tripped

There is NO spark whatsoever. It just turns over forever.

I have adjusted the timing every degree for 10 degrees in each direction and
there is NO spark.

Since I have replaced everything electrical that I can think of, and there
is still no spark, what else is there to do?

It has fuel. It has air. And all the electrical parts are new.

Previous owner inisists it ran fine when parked three seasons ago
(naturally).