I've been looking online for flying guides and found several for the C337H.  Thing is, several of them mention manifold pressure and the ones I've found mention that, for the H, it should be 35 Hg on takeoff.  This model's gauge doesn't even go that high.  The D model info I found mentions manifold pressure of 25 Hg...top of the green arc.  So, is this a D?

 

Gregg

The C337G owner's manual I have states 15-25 in. Hg (green arc) as normal operating range.

And http://www.avsim.com/pages/1111/Carenado/337.html contains:

Our simulator model is based on an H model that was built in 1975.  In my digging around for specific performance information, I came to the conclusion that you could use the ‘G’ model performance data and be 100% accurate for the simulator model.  There are only a few minor differences - the one that is most noticeable is the addition of the large baggage door.

 

And when looking at the fuel pump switches and fuel capacity, it is the long range version.

 

I guess you found values for the T337H (turbocharged).

I think the D version has a more complicated fuel tank setup, too.