Just a comment about parts and using parts from older machines.
It's quite common to use parts already approved on another machine as they don't need to undergo an extensive (read $$$) approval process. The company also doesn't need to put in another part number into their supply system. There's less chance of screwing up and getting the wrong part number, and so on.
I remember being slightly shocked when I started work at Bell in 1984 on the model 400 (anyone remember that?) to find out it actually had Bell 47 part numbers. But I quickly understood why.
In the 429, Bell did use a 'clean sheet of paper' approach, and only used older model part numbers where appropriate. It is a new design.