Electrical system for Champ 7DC?

Hey everybody,
I'm new to the Champ culture, but I'm learning fast. I'm considering a
Champ 7AC, converted to 7DC with battery and starter.

I am an A&P, and I want to get an idea of what it would take to install a
full electrical system to power a radio and transponder.

I'm thinking about the gear driven B&C alternator, if the STC exists. I
understand the transponder issue, can't go back.

I guess my big question is how to do the paperwork. Is there an STC for the
electrical system? Do I just go get a field approval from the FSDO?

Thanks in advance.
Jimmy Cash