It's tough to put a value on a vehicle like that. They don't even feature in British classic car price guides (I looked). It's almost a case of it being worth what someone is willing to pay for it, but most importantly what kind of shape is it in? Value is in the eye of the beholder, and if it's in beautiful shape it will be worth a reasonable amount. A pile of rust, no matter how rare or unusual, is still a pile of rust. I'll do some digging, see what I can find out.