Hi Steve,
My name is Roger and I live in the US. I have been building a 750 Beryl for about 3 years now and maybe I can answer some of your questions. There are pictures of my Beryl project in the photo gallery here
http://www.avions-piel.com/galerie/thumbnails.php?album=48I changed the fuse tubing interference at the rear control stick you are refering to, there is a picture of the changes I made in my photo gallery, actually there is a before and after picture....
I too was told the wing incidence is to much for the 150 hp+ engines. I was told it was designed originally for a 100 hp engine. I changed my wing incidence to 2 degerees " i think". Which required changes to the tubing where the wing attaches to the fuse. I would need to look at my notes to be sure about the incidence I used.
The incidence for the tail is "0" And yes, the top longeron is the datum. There are no changes needed to the landing gear because of the wing incidence change, that I know of..
I was told that the CP751 was used for Beryl's with 180 hp engines.
As far as the differences between the wing and spars from the Beryl and the Cap 10, I have asked that same question but haven't been able to find anyone who could answer it.
There was a change in the plans for the wing of the Beryl some years back. The wing spar has a plywood doubler added to the center section to strengthen it and I think the wing tips were shortened some by being squared off more. Just be sure you have the revised drawings for the wing before you start, the old plans wing and spar are weaker.
I hope this helps you some, if you have any more questions just ask them.
Roger