+1 for CLH. Go speak to Chris (founder). He's a walking encyclopaedia on trailers and parts, and also has a workshop full of pukka metalworking machinery.
I have phoned CLH and the guy was very helpful
At least 1.5 hours away which is ok
The engine will need to move forward and back
I may need to put concrete at front so it is balanced correctly
Also I intend making it curtain side
There has been a large amount of one-offs made by members on this site but I doubt anything like this
There may be another one-off to follow
Thanks for all replies