im thinking you mean
fingerboard radius? Well if you look at a guitar fingerboard it isnt perfectly flat; its curved, lower at the sides and higher in the middle and this is the radius of the fingerboard. The 400 simply means that the curve on the fingerboard is a section of a circle, of radius 400mm (if you get what i mean

) The larger the radius, the flatter the fretboard is.
I dont really understand what your asking in the next part of your post but if it is what i think it is (can I use this neck with another body, and if so how will the radius affect this) I think the answer is yes, you shouldnt have a problem using the neck with a new body, as the radius only really effects the way the guitar feels to play. i think

(can anyone correct me here?)
-better shred than dead-ANDY