The beam is not a "problem". I have seen 55 foot boats 10 feet wide--and even saw one 8'6" wide. They tend to roll a bit more--and are not as stable, but are very effeciently driven through the water. I have owned a 29 foot sailboat with 8'6" beam--and it was very satisfactory. You get a bit more room in a 10 foot beam--but have to have a permit to trailer it. Plus, trailering a wide load is a bit of a hassel (in my opinion--I have done it).
As for displacement vs weight. The CMP has a stated weight of 11,000 lbs--who know what it really weights--until it is weighed on a scale. This is a true trawler speed boat, and will be very effecient at that low speed--not an "express" trawler.
Here is what David Pascoe says about weight vs displacement:
"Weight -vs- Displacement
The weight of the vessel as could be measured on a scale versus the calculated displacement are not quite the same, though the difference is not enough to concern boat owners. Displacement is the volume of water that is displaced by the hull of the vessel measured in pounds or tons. This derives from a math calculation made by naval architects during the design process. No one actually ever physically measures the displacement of a hull as that is far too costly to do. Displacement as a representation of boat weight is no longer used by pleasure craft builders, though it is always used for ships.
So where does the builder weight come from? Commonly stated as "dry weight," it normally means the weight of the boat without any fluids in tanks. Since most builders end up having to ship boats, which requires obtaining an actual measured weight, builders typically ship the boat off to a truck weigh station where the weight is there taken less the weight of the trailer. These weigh stations, operated by federal or state governments, are actually quite accurate to within 100 lbs. The scales are tested and certified annually."
I would doubt that a 7,000 lb boat would displace 11,000 lbs, unless there is a serious error on the NA's part.