As the other guy said - there is NO engine clutch. If there was - sticking or dragging would not cause your problem anyway. It's a powershift type reverser with hydraulic powered clutches. The term "powershift" denoting the ability to shift on the go, under power, without touching the clutch pedal.
Your's is dragging enough to make it hard to get the gear trans into gear. Try idling engine all the way down to the lowest speed and then try to ease into a forward gear. If it clashes too much try easing into a reverse gear. A little clash is normal but it should ease in with the engine at idle speed.
What happens when you are in let's say 1st gear in forward and you push in the clutch? Does it stop with the engine running freely, or does it want to keep going and when you hit the brakes, the engine labors? If the latter, the clutch discs in the reverser are warped, or the center-bearing is burned up (very common problem). More common in 350s, but happens in the 1010s as well. The reverser has a tiny cup and cone bearing assembly between the input shaft and output shaft. It takes a real beating when using the crawler hard in hydraulic reverse. Later on, in mid-range 350s it got upgraded and enlarged.
And yeah, you also have to make sure the clutch linkage is working.
If it's dragging, put a gauge in the clutch port (under your left foot) and look for 120-130 PSI when the clutch is up and 0 PSI when it's down. It's the same thread as a grease-gun hose. So a 200 PSI gauge hooked to a grease-gun hose is all you need.