AD Restoration issues

[Roy Johnson]

This machine has not been run for 30 years before this year... https://www.youtube.com/watch?v=GeOo_FeMfbU&t=163s
Gear change is very stiff. Have taken the top off the gearbox and CRC'd (WD40) the fork and rods and emery papered where I could get to. Checked oil. very clean anyway and added some more SAE40 to front compartment. Still very stiff. Do you think it will come right with use?
Also clutch has a 2-3 second delay but better at an idle. Have filled cap on right hand side with grease. This too still no better with a bit of running.
Any tips without splitting it?
Cheers Roy Johnson