Thanks for the links on the fairing. Good price, too!
I have a nice set of PIAAs from my Brittania fairing on my 690 that would work great in that.
One thing that is always an issue on DS conversions is getting frame tubes that go under the motor to support footpegs and a skid plate. I've thought about it long and hard. One solution is a removable cradle section. I made some disconnects, but they're fussy and heavy.
Your tonsil shaped part ought to work OK if you have a tube that does under the motor and ties into the frame there. Before you weld everything up, make double-damn sure that you can get the motor out. I know this because I did a pretty cool motor swap for a guy -- a KX 500 motor into a TZ250 chassis -- and got one of the motor mounting pylons angled wrong and the dummy motor wouldn't come out. Oops.
When they say Harleys are for 1%ers, I don't think they mean guys who sell crank and get in bar fights any more.