I would also suspect the computer as per your description.
Everything checks out within specs but it won't run, yet there's no
codes (a malfunctioning computer likely would malfunction in providing
codes as well).
FWIW: My '89 Z24 convertible wouldn't start when I got it out of the
barn for spring. I ended up having to clean the crank sensor connector
as they get oil-fouled and prevent starting. There's a TSB regarding
this crank sensor connectctor issue, although your situation doesn't
sound like that at all. I just mentioned it because your situation was
similar to mine (car sat for awhile, same engine, year etc.)
Another episode with that same car resulted in extensive checking of
systems, sensors replaced, etc., still wouldn't run right, finally
determined the computer to need replacing (no codes due to this).