In doing this, I learned that older style DUPLO bricks are not compatible with the Quatro bricks. There is a reinforcement piece between the tubes on the underside of the older style DUPLO bricks that interferes with placing the DUPLO bricks snugly on the Quatro bricks.
those Technic pins
Yes, those are basically 2×4 bricks with pins on the end for attaching wheels. The only part that looks like I made an effort was the top of a yellow train station that I disassembled yesterday. 🙂