I know you can go onto Ebay and get 'sold' cars to show up. That is a 'real' comp.
In the end, with such a well-maintained engine, it's something that should be considered for a 'buy-back'. After all, if the adjuster is going to low-ball you, maybe you could get him to make the purchase of the car a real steal.
I remember one engine we put back together about 5 years ago, that no sooner did we get it back to the customer, but his son drives through a stop sign at a 'T' intersection and totals the car. That engine was PRISTINE.
I told the owner to buy it back, which is within your rights under insurance company rules. Before he could move on it, and I mean in just a few days, Allstate grabbed it up and delivered it to the salvage resale lot. I bet the buy-back on this car was no more than $500, on an engine that just had $4000 of work done on it. The block/ head were perfect.
So, if they aren't going to consider the engine's value for settlement, neither should they on buy-back.
Moral of the story: An engine removed is often worth more than the car it came out of.
Know your legal rights. I hope it's not already gone...check and see. Let us know.