Are there no remote reading instruments which will work with the Avidyne kit?
Presumably the ADF needle will display in the "RMI" presentation on the MFD?
The dual-box RHS cutout solution was done as far back as 2002, IIRC. It doesn't look great but is OK if done neatly.
Re insurance, you could ask your broker. His reply is likely to be "you have to be legal" because that is what they usually say, but you could ask if they ever avoided a payout on the basis of equipment carriage. I've never heard of this having happened myself.