No I doubt they will fit. The lug pattern is probably completely different. Also you must take into account center bore diameter, backspacing and offset as well. Also the wheels on the 68 thunderbird are most likely standard. Everything back then was standard. Nothing was metric.
Well there is one way to find out. Pull a wheel and try it. Still remember your backspacing and offset. You don't want to be hitting the brake components or the wheel offset is so far it makes the car ride differently.