Colin,
I think you're on to something....Although I went out of my way to "try" and find the right shocks initially, it looks like I've ended up with standard length shockers.

I took the bottom pin off today and extended the shock fully. It was only about 10mm past the mount when fully extended, so I'm sure that's the banging.

I've just ordered some One Ton front shocks which should be here mid next week. I'm certainly hoping this gets me sorted....

Cheers!
JRW