Your clutch disc could be stuck, but here is another thought: I am using a T5 from an Astro / Safari van and an 11 inch flywheel and clutch. The Astro van clutch was much smaller in diameter and naturally had the proper spline, but that clutch and pressure plate used the short throwout bearing. I used the short throwout bearing in mine. The longer one will not fit...or at least it would not fit in mine. Then I learned the linkage was too long to allow for proper adjustment. If you look at yours and if the adj nut is almost all the way to the end, you have the same situation. So what I had to do was make a new clutch connecting rod. From 5/16" rod I copied this:
http://i1154.photobucket.com/albums/p535/JonGoodman/IMG_8524.jpg
but made it about 3/4" to an inch shorter and that gave me all the room I needed. You can see it here but not very well. Bending it was not much fun:
http://i1154.photobucket.com/albums/p535/JonGoodman/IMG_8522.jpg

Good luck!
Jon

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end