Thank you. Sorry for the delay
The metal (instead of plastic) body doesn't really change anything, it would be like converting any other Athearn diesel. You'd need to remove the motor and isolate it (like with electrical tape) from the frame, and then solder the connections from the track pickup and to the motor etc.
Many books and online sources are available on Athearn DCC conversions since those engines are so plentiful and have been around for long.
Has anyone every converted an Athearn F7 with a Cary metal shell to DCC? How do you insulate the decoder from the shell and frame? These ran good on my DC but I am converting it to DCC