I bought the rear Asso axle (RC12R5.2) trying to fit it into my R12C.
I have to say that can work but there is need to change the carbon plate.
Cecking this post
http://www.rctech.net/forum/11460858-post426.html we can see that the chassis has a different offset so when I use the Asso axle it is more width of about 4mm (2+2mm), i had to use shims for like 6mm on the left side and 0 on the right wheel
I think the Asso Axle can work but is better to have the carbon plate that is not what I/we use on the R12C..but i don't know which is
I hope this can help you, i'm sorry for my poor English.