You might want to try Hagerty Insurance located in Traverse City MI.
I had all my streetrods insured through them and I now have my '76 FLH fully restored through them. They offer great coverage and road service or trailer service as well.
They do collector cars and bikes. They may not want to fool with a "custom" production bike though. What harm will it do to call them or get a website quote.
http://www.hagerty.com/They've treated me well and I know they have treated other with claims very quickly and honestly.
I get confused on this, but I believe they do "Agreed Value" for vehicles. State Farm does the other, "Stated Value". I know for a fact that State Farm has the lowest prices, but I've been first hand with their claim service. With their stated value they have the option to replace your ride with what they feel is comparable in price. You have to almost sue them to get what you think they promised you.
Hagerty on the other hand will pay you to fix your own ride. They won't pay you shop rate, but will pay you an hourly rate that more than covers your actual costs to do the work yourself. If you have a total, they will pay you what they agreed to in writing. State Farm will use a current value similar to the value on the policy and you have to fight with them to get it.
A buddy of mine had a really nice '29 Brookville steel roadster and had it insured with State Farm with a stated value of $30k. He was paying like $175/year for the coverage. At the time I had my partially built streetrod insured through Hagerty for $40k and I was paying just about $500/year. I later increased my ride to $80k and it was about $800/year for full coverage with all the extras. So for the price difference what do you think you're going to get in a total? That's why I went with Hagerty on my '76 FLH as well. I have it for $13k and I pay $279/year for full coverage and the extras. I had higher quotes from standard companies so Hagerty was a no brainer.
I'll be going with them, or I'll try to, on the new boardtrack racer when completed. It just makes sense to me to do so.
Give them a try and see what they'll do for you.
Good luck.