clutch won't depress on 78 4 speed

I have a 1978 ford f-150 4x4 with a np 435 and a 390. Now my clutch pedal will not go in. If i take the linkage apart it will work freely, so i checked the fork going into the bellhousing and it was fine. It is something in the clutch its self. Could someone please help me out. I really do not feel like taring it out unless i am going to put in a new clutch, i hope its something simple.

if you have a torsionally damped clutch, there is a possibility that one of the torsional springs has fallen out of the clutch center and is caught between it and the flywheel. I have had this happen on about 1/2 dozen spring dampened clutches over the years. not a pleasant prospect, but another suggestion.