Here's a bit of an update,
I contacted PS and they can't supply the hubs.

He suggested that I contact George Petrus which of course I already had.
I contacted George again as his contact hadn't come back to me, George gave me the number for Bullet Fabrications in California who he has authorised to produce the Cobra parts.
Unfortunately their website is down and they are not answering calls or messages.

I have however discovered that the UK Kirkham agent (Hawk Cars) do a 6 pin drive hub based on the Jaguar upright.

Not cheap but available.

I still haven't located any E Type uprights so I'm starting to look at XJS ones, which I believe are similar but the length is slightly different, they also have slightly stronger stub axles.
