First off, a 302 didn't come in a 68 EB. They didn't start putting 302s into the Bronco until 69. So that right there I would play that the dealer doesn't even know what he has. Play it up big. Also, tell them that it has the weaker front axle (dana 30) and it has vacuum wipers. If it has electric wipers then someone has done a conversion on it. 68 was the last year for vacuum wipers and that can also play into your hands because again, if he is listing it as something it is not, well.... Basically, if the vehicle is in good working order, good body, etc. then I would low ball the guy and play with him. Most of the time when an EB is at a dealer they can usually get a decent mark up because they are in demand. I saw one in a Volkswagon dealership here in Colo. Springs that was no where near as built or good looking as mine was and it was listed for $12,500. It sat there for a looooooong time at that price.
Best bet, if there is a website where the car is listed, then post it, let us look at it and we can all give you a better idea of what to go in and offer. Most of us have had at least 1 or 2 EBs and we can tell you what to knock off on price, etc. That is what we are here for. If we can help you get it for a steal, then by all means, we will. So post the website so we can take a looksie.