we do DIY when we can't find similar parts in the market.
ATM and Eagle Racing now has SAS for the rear of the car which is similar to what u are doing.
so why not modify from available parts, maybe u can use two sets of SAS and Diy the chasis and centre transmissions.
btw, don't use so many nuts, juse 2mm king pins plus spacers.
u can consider overland, F1, monster, mr02 stainless king pins, they are all of different lengths.