If you built it and you have all the receipts, total them up. Not sure how to judge your time but maybe shop around and see if you can find a builder to give you a cost for an actual build. The total would give you a new replacement cost. Then maybe shop around for 302 FFRs for sale. Ad or subtract differences. Take all of this to a knowledgeable Cobra dealer (maybe ask FFR for recommendation, ask the guys there in Portland selling Cobras at
www.shelby-cars.com). You are going to have to pay someone for a professional-estimate. Maybe show these options to insurance company and see if they will accept a paid professional estimate. Sorry to hear you have to go through this.