There are plenty of certified engines flying around that are much older
than that (and I would trust those too). Do you think Contintental is
still making A-65's to throw into the Cubs and Champs that so many
people still fly? Given that a Corvair conversion done according to
established plans (by William Wynne) will be completely rebuilt and
with many new/specialized parts, it's largely a new engine. There are
a LOT of them flying in experimentals these days. There have been a
few issues with the crankshafts (no major accidents have resulted from
this), but with nitriding the shaft it should be fine.

As to finding one, as is often pointed out, GM made more (several times
more) Corvair engines back in the 60's than Lycoming has made of any
engine during it's whole history. Finding them is quite easy. The
usually sell for $300 or less. You'll have to dump another $3k or so
into it to get it airworthy though.