I'm always eager when reading forum posts to see how the suggested solutions to the posted problems turn out.
I was the one to initiate this thread, so I wanted to give a long-term update.
The head works great! It no longer smells, ever. It took about four good flushings of fresh water/vinegar over two weeks to flush all the crap through.
Luckily the previous owner had tapped the head seawater intake valve into the sink thru hull
so with a very easy switch of a lever to close the sea cock, I can pour the vinegar solution into the sink and flush it through the system.
We use the head every day, pump with sea water, and it goes straight overboard
(I hate it, but no place to pump out way up here), and it NEVER smells. I keep a jug of freshwater/vinegar next to the head and every few weeks flush a liter or so through the system. It keeps it unclogged and clean and smelling like roses (or...vinegar...).
Peggie, Head Mistress, You are my hero.