Just bought a nice series 2a swb, it has had a rebuild at some stage but has sat for about 3 years, The only problem i could find while drivein it was, the clutch was extremly heavy and there is like a delay when you bring it up and it lurches, i replaced the slave and master cylinder and greased the joints there is no change any idears before i take the box off?

Yep
Drive it for a few weeks it may free up with use.

The linkage was always a problem, also it might have an earlier clutch cover, multi coil spring type fitted.