It is going to depend on your state and which insurance companies you go with. I could not find any insurance co. in NJ willing to insure the car as a roller because they did not deem it to be a "car" until the drivetrain was installed. The only option I was left with was adding it to a personal property rider on my home owner's policy, which was a hassle and not very cost effective.
Since Intercity insured it for full value until it arrived at my door, I didn't think there was a lot of risk leaving it uninsured for a couple of weeks until I got the engine installed, so that is what I did, but I was extra careful to make sure the garage was securely locked!
My policy is apx $600 year with a 3000 mile limit.