Asked the seller why he went with a 20hp motor. He replied that he bought a 27 but it "wouldn't fit in the hull" so they went with the 20. Hard to believe that with all this space (gotta love the access!) they couldn't make a 27 fit.
He claims 20hp is plenty, especially since it's a diesel (there is that diesel vs. gas hp thing again). Yet, he also said he didn't think he was using the extra hp with the A4 anyway.

Not that it matters, she's got 20hp and that's that. But it does throw the credibility of the claim that 20's plenty into question.
Would have made more sense if he said, "We never used all the power from the A4, so we decided on 20hp for the refit.
Conditions could be benign during a sea trial and it might be hard to determine if she's under powered.
You guys buying the "wouldn't fit" excuse?
Edit: After I posted this, I decided to post the same question in the diesel forum.
Could 27 hp fit here?