Thanks for the input guys

As Curly and Huvius have said the ideal would be to rechamber to the original .360

I will try to find a good smith who can make an insert (it is 12mm x 54mm parallel [.470 x 2.13"])
so would be relatively straightforward for the .400/360 2 1/2" without re making the extractors but will take advice on that and whether a simple chamber insert would be OK
I would only shoot BP in it anyway

Tony