I was very pleased to hear you are considering building a Shadow.
The double berth in the drawing is indeed only there when you use the deck tent. Incidentally, the Shadow has a solid cockpit floor throughout, not a trampoline.
You could fit a solid cuddy as we did on Tucanu. The basic drawings are on this website, follow the links from the Plan Updates page.
It will be pretty easy to do on a Shadow as there is already a deep mastbeam, a solid cockpit and the jib sheets go to the mastbeam not cockpit.
The prototype Strider was narrower, but then we drew the boats wider. So I have no objection to making a Shadow a bit narrower. You won't have any stability problems as the Shadow has a small rig.
I hope this answers your questions