[icegreentea]

The spinal nerves (by and large) originate in the spinal cord at their level of origin. That is to say that if you severed the spinal cord at some point, you could not 'split out' the connections corresponding to the lower spinal nerves from the overall bundle. Amongst other things, the spinal cord also contains neurons that form closed circuits without reaching the brain (these make up your reflexes).

So, if you transplanted the head and spinal cord, then use, you could somehow make '62 connections'. If you transplanted 'the head' you would have to join the entire spinal cords.

Finally, each nerve is really 'a cable bundle', so the process of joining them is kinda tricky, and beyond the scope of my knowledge. Needless to say, the authors of the paper think that it can work. Their references likely can point you in the right direction.