I've just renewed my insurance with A-Plan.
They were happy to ensure it before I got it on the road.
( Although it had to be over 90% complete first due to the 'alfresco' nature of my build.
)
They agreed a value when it got on the road while still in grey primer.
They have agreed an increase in value now that the car is painted.
They just require a specific list of photos to go with the valuation.
Hope that helps, Paul.
PS
I agreed to a limited mileage policy, but the mileage limit can be exended if required.