Plastic
> wood is not, as yet, being marketed for historic preservation
applications, as
> far as I know.

Not quite true. How about columns and their plinths and capitals? There are
also a variety of plastic  and HDF versions of Victorian ornamentation on
the market. And plastic examples of plaster decoration like medallions can
be found in even otherwise well-executed restorations.

And, I once made a couple of dozen fiberglass replacement panels for a
partially rusted out tin ceiling that was the result of an earlier
renovation to a Greek Revival church on the NRHP. Thirty feet up in the air
and no one could tell the difference. It wasn't just a matter of saving
money. The only fabricator who was prepared to undertake the job, which
would have involved making dies for two different otherwise undocumented
panel styles, wanted a year and a half to supply the product. The bank
holding the reconstruction loan  insisted upon completion and conversion of
the loan to a mortgage in less than 6 months. It was a simple matter to
remove two of the intact panels and use them as molds to vacuum-form the
needed replacements.

Another ethical quagmire?

Bruce