If you can find a chassis cab of the right track and wheelbase, it should therotetically be very doable I would have thought. Or are you planning on taking the entire rear (body and alko chassis) and connecting it to a new cab front (bit like a cut and shut in a way?)
I would really check hard if the existing motorhome body is solid enough to warrant it. They are typically not the most robust things and once removed from the existing chassis if that were the plan could become extremely wobbly! An transplant of the interior into something like a low-loader luton could be an interesting option? give you the opportunity to rejig and refresh anything.
Intriging project