I've recently brought my old Model B out of semi retirement, added a PM5 monitor and RowPro software and started on a quest to get fit again. I've added additional cowling to bring the drag factor down in line with the later models and designed this attachment to allow easy adjustment of the vent across its full travel from the seat.

Also see my scale for the model B - http://www.thingiverse.com/thing:1449048

The green one is my prototype, the black final version is printed with 4 shells, 50% fill and the temperature raised a bit to increase strength.
Drill 2 holes in the disc to attach : see photo.
Attach the lever to the mount with the top bolt before putting in the others. Getting the nuts on is a bit fiddly and you need to flex the disc a bit and get a finger behind to hold the nut.
The bolts need to be cut off flush to the nut so as not to foul the cage; I used nylon bolts and sliced them off and also added a few spots of brown gorilla glue to get rid of any play.

Check out the Concept 2 forums for a lot of discussion about drag factor : http://www.c2forum.com/