I have a tank off of my 01 Road King with a minor dent. Has the gauge, panel and 61 circa badges. I went to 7 gallon after bike was ran into a guardrail. You shouldn't have a problem getting some coin for your fairing.
Just sold my fairing and most of the stuff with it. Inner,outer, brackets, gauges, trim for 700 to a local buddy.
Took the frame last week to Harley. had new bearing and races installed. Next week will the Roadking Main harness. Also got a bunch of arp bolts in the mail.
Sweet build. I converted my 07 Road King police bike into a custom Road Glide. You're doing it the right way. Get the correct wiring harness, and just build it up as if it came from the factory as a Road King.