There is no "technique", its called common sense. The car is missing its original front end, you don't toss out the front-end of a classic car and "retrofit" something which doesn't belong there unless there has been an accident.
Secondly the car doesn't look geometrically straight, its obvious from the pictures, whoever repaired it did a poor job.
Anyway if you have an offer of 85K, you should sell it before the buyer changes his mind. If your deal doesn't materialise, my offer stands.
Good luck (y)