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The OP wanted to reshape some of them oval to fit two new caps in. I
would keep the can intact. In other well-developed collecting areas
like firearms -any- modification including refinishing reduces value.
I think the practice is to save the original parts for show if you
want to make the device functional. That's what I do based on museum
exhibits.

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We run into the appearance/ functionality/ safety argument regularly at the
museum where I volunteer as restorer of old machinery. Steam powered stuff
is a real problem as old boilers weren't built to codes and are difficult to
get registered. Riveted boilers are a real problem if the barrel isn't
covered with lagging and cladding. I know of one boiler on a replica steam
boat that has rivet heads attached to the boiler with high temperature
adhesive. The boiler is of all welded construction and the rivet heads are
just for appearance. I have been known to slip in stainless steel components
occasionally to reduce the corrosion and maintenance. They aren't authentic,
but they save a lot of maintenance time.
We have a significant steam traction engine to restore in the near future
but the boiler is beyond repair to the extent that it could ever be safely
operated. We have accepted the fact that it will never operate on steam so
we will bypass the boiler and operate it on compressed air.