We don't sell separate backs and bodies. When you buy an H4D it is sent to you as a package, calibrated tested and ready.
Its not a quick visit to the NY office if you live on the other side of the USA, or if you live in Australia and your nearest service centre for adjustment is where???
Should an H4D owner think they would like a spare body then 9 times out of ten they order it when they order their H4D. The two bodies are then calibrated together.