Hi,
1/24 is waay too small. As Mike indicates the scale based on pilots is around 1/8th...ish. When making the patterns for the SS Speeder I tried various scales of figures to see which scale looked closest to the ILM pilots.
1/6th was too big, 1/9th was too small. Hence something in between. The studio model pilot figures were sculpted from scratch by ILM as there was no handy popular figure scale that worked for them. I had to sculpt my pilots from scratch too.
Thing is, what are you wanting to match to? The ILM models scaled up to life size. Or trying to work out the dims of the Elstree live action props? There are big differences between the two. On looking at on set pics with the crew near the speeder props I tend to think that the scale of the figures in the ILM models are actually a little big compared to how a person looks next to a 'real' speeder prop. Certainly if you try and extrapolate a full length person inside the SS Speeder model you struggle to find enough leg room. The ILM figures only needed to go to waist level so this never became an issue for them.
Alot of my stuff is in storage or I would post up the Elstree set pic showing the crew next to a speeder. Maybe you have this already?
Cheers
Nick