You are very kind to help.
The original is 5 inches tall, and I am afraid a 10 1/2 inch chimney would hit the bulkhead when the boat
I did find a 1 5/8 inch chimney, 4 1/2 inches tall on the site you linked to. I am thinking an adaptor cut from a tin or aluminum
can might shim up the lacking 1/16 inch, or I can bend the little metal "fingers" that hold the chimney, toward the center. .. They are cheap
at $4.5o, so I will order two of them, and see if I can make a simple adaptor ring, or circular band shim.
They appear to be the same shape as the original chimneys.
I'll post the results.
Thanks again for the help.