I got a bit of time in the workshop today and managed to get the front axle mocked up, can anyone give me an idea of a suitable maximum steering angle, at the moment the front wheel turns about 35 degrees before it hits the leaf spring.  I’m not sure if this is enough?

Personally I'd say that's way more than enough. I would be restricting it back from there!

Looks perfect to me. Plenty of steering is useful especially in the wet if you get the back a bit to wide out!