
Even fewer insurance companies than finance companies understand warbirds.
Cannon Aviation Insurance has a nice program that offers a discount for training and encourages participation in the Red Star Pilot's Association.
There are a few more out there. Some won't insure the hull or the crew. Get the maximum you can.
Be sure to find out their dual and solo requirements. A low time pilot (<500 hours) may be required to get 15 hours dual and 5 hours solo prior to carrying passengers.