Used the Redux i/f to exchange the DOU for IOU-2. All is well.
All VALID Assignments:
A-13: IOU-2 base: cost of $3.00 and a weight of 8g.
A-6: a bobbin with a cost of $4.00 and a weight of 4.0g.
A-4: IOU-2. This has a cost of $5.00 and a weight of 2.0g.
A-3: parts list that is compatable with an IOU.
A-2: objective lens has a weight of 1.0g and a cost of $10.00.
A-1: 1 mirror with a cost of $1.00 and a weight of 1.0g.