Are you going to add bed strips? It would be real easy to do, except for all of the drilling in the aluminum. With some careful planning, you could predrill all of the aluminum on a drill press before assembly. I would make the holes larger than the bed strips bolts so that it will be easier to fish the bolts down through the cross sills.
BTW, you do not need to worry about having a groove in the bedwood where the bed strips lay like original bedwood. The bed strips work just fine laid on top of your flat boards. I did one of my beds with those kind of deck boards. It looks just like it should.
