evaluating aircraft

Guys, thanks in advance for your help on this one. My airplane was lost in
Katrina (more on that later), and I am looking at buying a quarter share of
a local plane. I am trying to get a decent idea of the valuation of the
aircraft, which is a '79 Archer II. I have run the numbers on both the
National Aircraft Appraiser Association (NAAA) through Trade-a-Plane and the
AOPA's website, Vref. The NAAA is much more thorough, allowing you to
define each avionic, specify damage history, exact times for engine and
prop. The Vref is much less comprehensive. The results are vastly different.
The NAAA values the airplane at $61K while Vref values it at $73K. I didn't
expect them to be exactly the same, but that is a huge difference. I suspect
that the true market value is somewhere in between, but where? Any ideas?