Each dealer has their own policy on working on "old" cars. Much of it depends on whether or not you bought the car new from them, or have bought newer cars from them since. If you have a reputation as a good customer, they'll probably gladly work on your older FoMoCo car. But they do have liability concerns....getting parts for old cars, having techs that still remember how to adjust points, set the idle mixture, etc. Anymore, most dealer techs are younger than the cars I want them to service. I finally sold my '65 T-Bird, but it would freak out the techs, since the car was probably older than some of their Dads. I also had a '52 Ford F-2 pickup that NOBODY knew how to work on.
Also, the dealers are cognizant of the fact that owners of older cars may not have the capability to pay for major repairs, and they don't want to get stuck with an old clunker if the owner defaults on the repair payment.
If you already have an established relationship with the dealer, I imagine they'll be happy to service your older Ford product. But if you're young and fresh off the street, they'll understandibly be dubious about taking on your car.