Your machinist will have to make a special right angle cutting milling tool to be able to go down and cut the internal splines in hub and also pass coolant thru it also, that was one of the biggest hurdles also the machine time on the hub itself was like 12 hours if I remember correct, the springs I have a few extra cause I had to make a 100 min run at a spring factory, that was over 5k$ , as for roll pin, locking snap ring bolts small parts I got from Mc master Carr . Good luck I hope y'all succeed. If it would of been casted it would of been cheaper but you would have a bunch made to justify the molding cost. It will not be long before 3D printing will be able to make this in a few hours, I am already printing 3D in PEEK AND PEI with carbon fiber which has a 400 degrees celcius melting point and can replace most aluminum. The technology is coming fast and I am 55 so I am slowing down, time for the new gens to take over.