Converting HO Spectrum DDA40X's to DCC

[Hskerfn]

Has anyone done this? if you have, could you pass on the info and detailed instructions as to how it is done?   What type of Decoders?   With all that board work in there, it is quite confusing!!!   I'm not going to attempt it until I hear from someone.  Thank you!   

[ABC]

But, they already have DCC, so why do you need to convert them???