So, my questions to any who care to answer a Is Fred right that the
automotive part is just unsafe and unacceptable?

Absolutely.
Don't go anywhere in that boat until you replace the carb and the non-marine
fuel connections. Better check your alternator, too.

The reason that marine carbs, alternators, etc etc developed over the years was
not because somebody wanted to make a big buck selling specialized parts. It's
because gasoline vapors in an enclosed environment can be *explosive*. The
combination of screwball fuel lines and an automotive carb has turned your boat
into a floating bomb.

Gasoline boats can be acceptably safe, *if* the proper equipment and
precautions are in place.

Even if it's safe, are
there other disadvantages? Would it be adequate to merely replace the
hoses with proper ones and install them correctly?

Not unless you can modify the carb itself to marine specs.


Are Fred's prices
reasonable? He's quoting $400-$500 for a remanufactured Rochester 4BBL,
about $100 for the spark arrestor, and the remaining $300-$500 is for hoses
and labor.

Will depend on your local market. I don't know carb prices, but the labor rate
seems pretty reasonable. Marine mechanics all carry what I think of as the $100
tool box.
Just to get one on your boat, tool box in hand, is going to cost you at least
$100 one way or another. That's before the real work begins.

Do the right and safe thing. Fix your boat.