just wanted to report from my next locomotive project - a KTM Union Pacific 4-6-6-4 where I just finished cutting tires. Making use of the advantages of "mass production" I found it a good approach to also do the wheels of the KTM 4-8-8-4 that are and exact match and therefore I can use the tooling for both models.
By studying some close up's of the 4014's big drivers I found out that the castings are missing a very visible detail of the original drivers, the actual box spoke backside. It took me some time to figure how they are constructed but there's a lot of info out there, also from the construction of the first driving wheels of the PRR T-1 by the T-1 Trust.
I use thin brass sheet material that I drill out for brass tubing that is soldered in place and then trimmed and cleaned up. Since the wheel centers are cast material that can not be soldered I simply used CA to glue them in place. On the Challenger these are not so visible since the first driver of each engine is behind a lot of rods and the crosshead but it really makes a difference.
Next step will be the drive train where I'll try to implement two motors for individual freedom of front and rear engines. Two decoders will produce independent sound and hopefully smoke. Also have I never before painted brass, that's going to be the special thrill.