Is that it for the engine or can you get away with just replacing the
manifold?

jps

It's beyond the manifold.

Bent or broke a rod in #1, most likely.
Could have damaged the crank in the bargain. One risk in a single cylinder
rebuild is that *if* the crank is damaged, it may not show up until the new
rod, etc, is installed and the engine fired up again.

A new manifold would be $3k.

New manifold and rebuilding #1, probably
$5-6k. No absolute guarantee that there wouldn't be a crank problem.

Pacific Detroit used to rebuild these 6354's, but hasn't for a while now. I've
got a line on a decent core, (with a manifold just a few years old) and a
strong lobbying effort from an individual with certain influence to get the
rebuilder to do "just one more". Looked promising at close of business today.

Hope to be back up in running in a couple of weeks, and hopefully no more than
maybe $10-12k including r&r. We'll see.
Two important rules about boat repairs:
1) It will take longer than you expect. 2) It will cost more than you could
possibly imagine. :-)

This is a good opportunity to consider replacing the tanks, anyway. No problem
so far, but twenty-year-old black iron fuel tanks are just ticking time bombs.
The cleanest swap is to bring them out through the engine hatch- and removing
the engine is the biggest portion of the expense.

It's screwed indeed, but that's the breaks.
Nobody said boating would always be easy or cheap.