Hi Andy
I'm not sure how Adrian Flux approach Agreed Value policies but I have such policies with both A plan and Graham Sykes.
Provided the Agreed value was less than a certain figure (which I think was around the £20k mark) both accepted the owners valuation without needing any independent verification. All they required was a series of photos of the car and completion some of the cars details on a form.
If you need someone else to give you an idea of the cars worth I would suggest you contact the owners club at
https://jpsc.org.uk/index.php/jpsc-cars/leader
In my view an agreed value for a kit car is always a good thing to have. I'm sure the variation in market place prices for kit cars could cause a lot of arguments between owners and insurers in the event of a total write off.
Best regards
Neil