The CVO RG uses different internals for the front suspension, I think 1” lower but not 100% sure. I can say they handle very good with the 21” on the front.
I know Legend makes a replacement front suspension for the CVO RGs. It’s specific to the bike with the 21” front wheel.
You are correct. The front suspension on the CVO RG with the 21 is 1" lower than the rest of the touring bikes. This is to keep Trail and Rack the same with the taller front wheel. Its what I also had to do to my Fatboy when I put a 21 on it many years ago.
Yes, to the best of my Knowledge legends is the only company making a front cartridge kit for the RG with the 21.
The CVO RG with the 21 handles very similar to the other CVO's with the 19" including my CVO King. I have almost 70k mile ridding CVO RG's with the 21.