Can we make isoglosses?

[Bernd]

Can pox be a variation of pock?.

Yes, definitely.
Even in contemporary German, 'Bockleber' and 'Bocksleber' would be valid words. Considering there were myriads of local dialects and no formalised grammar in the 15th century, people more or less wrote words as they sounded to them so all those variations should not be surprising.
k -> kch transitions are very prominent in Tyrolean for example.
None of this definitely proves that 'pox' indeed means 'buck's' but considering the recipes it's not unlikely.

One alternative as pointed out in Aga Tentakulus post is that it's an expletive. It can either be derived from 'bocks' meaning in the devil's name or from 'gotts' meaning in god's name and can be used in an oath or curse, see 'potz-'.

So helf ihm box füdloch, box lüs

That's some seriously vulgar Swiss swearing here