1977 Land Rover Series 3 clutch problem

Transmission problem
1977 Land Rover Series 3 6 cyl Four Wheel Drive Manual unknow miles

clutch will not disengage. Cannot select gears with engine running. When engine off and gear selected and clutch pedal depressed the vehicle jumps forward on the starter motor a little as if it is being started in gear. I have overhauled and checked the clutch master and slave cylinders. There is nowhere to view what is happening at the clutch face. A friend has suggested towing the vehicle with the engine running and trying to slam it into top gear to unfreeze?