If the gearbox selected all the gears before you fitted the clutch then I think as Mark has said you have locked the mainshaft to the sleeve gear with incorrect parts between the clutch hub and the sleeve gear.
I think I have solved the problem! I stripped the clutch, as advised. But that is fine…..
Into the box, and after reading the manual it talks of the selectors getting seized. And they were solid! Not sure if lack of use. So took them off and cleaned them up. Will add some Amsoil lube to keep them fresh.
I have stripped the gearbox and looked at all the bits inside and gears. Stupid question ..... The pegs, looking at the manual I can see the peg nearest the clutch side sits in the bottom front slide face.
The peg nearest the gearchange, it says evenly spaced. Can anyone explain what this actually means, and if the peg needs to be set in a certain position? I just can't understand why it is - was jammed. I have no clutch fitted and all fitted inside correctly. Can only assume the dog and pegs need to be set some certain way.