It would seem that if you could find a relatively cheap pair of higher aspect daggers, it would be worth a try. I suspect it will only improve the boat's performance to windward.

For making a dagger board trunk adapter, I think either some hardwood (as long as it doesn't swell) or hard plastic, maybe 1" thick. I think I would just make templates out of the existing wells (if you have access to the type of boat your are getting your new dagger boards from, it would be real easy). Hold a piece of paper/wood/cardboard on the underside of each hull and trace out the opening, repeat for the topside. Transfer your tracings to the hardwood, cut out with a jig saw, and epoxy in the boat.

sm