Because of the nature of the Morgan front suspension you may need to roll the car backwards and forwards a couple of times to get the stub axle to settle into its static position.
Trying to bounce up and down on the front end will not be particularly effective because doing so would try to move the tyres sideways. It is for this reason that, when the car is not rolling, the front end of a Morgan seems particularly stiff if you try to bounce it. If you had the wheels resting on plates that could move sideways it would be a different thing.

When doing this sort of check it is also recommended to unfasten the bottom end of the damper so that that does not have an effect.

A simple way to check whether or not the lower spring is too short is simply to measure both springs. If one is just touching and the other is the same length obviously the lower spring is not the problem and it has to be stiction of the stub axle on the kingpin or a faulty upper spring.

If there is not stiction one of the effects of this would be more body roll when cornering to the left.

A thread on this a while ago, led me to believe that the rebound spring should just be touching the stub axle, when the car is normally loaded. Have I got this right?

This good advice is based on the fact that any static pre-load on the rebound spring will work initially in parallel with upper compression spring, dramatically increasing spring rate until rebound spring becomes unloaded. A little difficult to get your head around as intuitively the two springs appear to offset each other or work in series. You have to consider they work on opposite sides of stub axle though.

Any rebound spring pre-load leads to the afore mentioned high spring rate which then reduces to a much lower linear rate when only upper compression spring is in play. This leaves initial harsh ride followed by soggyness as suspension compresses further, exactly what is not required.

A rising rate compression spring would be ideal with no interference from rebound spring, but not sure if such are available.

Would that not be when cornering to the right Peter? since that would unload the right hand wheel where the OP has rebound spring play, reducing roll resistance on that side until the rebound spring becomes loaded.

Oh shoot! You are absolutely correct Richard. I'm so used to sitting on the left when driving I started thinking of the LHS spring as being on the driver's side. What's called a "senior moment" perhaps

As Richard points out it is when the rebound spring is loaded in cornering it inhibits the rise on that side of the car.

If its any consolation Peter your not the only one suffering from moments. Had to edit my first post on this thread to change left to right

I have never really accepted the idea that the rebound spring should just be kissed. I agree with Hamwich that the rebound spring should engage the bottom of the stub axle about 1/2". Every time I drove the +8 I would check the gap. Sometimes it touched the stub axle, sometimes there would be a 1/2" gap. But even when it touched I was always able to twist the rebound spring. I Emailed Mel Rutter who informed Peter Ballard. Peter stated that until I cured the "Stiction" (His term) I would not have a proper installation. I guess I have given up. Seems to ride OK and handle as good as any other +8. Sometime in the past I removed the cut rebounds and installed a new pair of un-cut springs. The ride was terrible. So there is something to Peter Ballards ideas IMO.

I'm not sure I understand what you mean, Button?

I'm with Peter Ballard on this. The rebound spring should be just free to turn when the car is at static ride height with the normal load (ie weight of driver).

If the gap is too big, you get a bit of a nasty 'tip in' effect when you corner, the car seems to roll more than it should until the stub axle settles onto the rebound spring.

I can't get my head round this: when I install a new kingpin I have to jack it upwards so that both springs are compressed before I can bolt it in place. There's no way I'd be able to turn the rebound spring at rest. Are the more modern cars (mine's 1972) different?

This article by Peter Ballard best explains Classic Morgan front spring characteristics. I have to agree that if you have excessive stiction of stub axle on king pin then the jury is out on determining static rebound spring pre-load or gap.