I am hammering the OED at the moment. Yes, it does look more like 'garn' than 'farn' and OED does quote a Northern dialect word 'garn' :
1695 KENNETT Par. Antiq. Gloss. s.v. 'Draw-gere, Yarn, still in the North call'd Garn; wooll workt into a thread.'
But would you have 'one Yarn'? Unless it means a reel of it. Again, why keep it in the cellar?
And someone more knowledgeable about farming practices than I am sent a message about the mysterious 'hayver' At first he went for 'oats' like you, Roger, citing the usage in words like 'haversack'. Then he thought oats growing in December were a bit unlikely so suggested 'heaf' instead, which means 'sheep pasture'. I OEDed it at once and blow me, all the citations for it are bang in the right geographic area - elsewhere in the country the same thing was called 'haft'.
'HEAF:
Accustomed pasture-ground (of sheep).
c1525 Survey St. Bees Priory in Monast. Angl. (1821) III. 579/1 A pasture for shepe upon the morez or hefe called Sandwith Marshe.' (OED)
Bearing in mind the 'ea' spelling in Tudor times usually indicates an 'ay' sound rather than an 'ee', I think this sounds likely, what do you think?
I had another look at 'bogge' and the second letter does look more like an 'e' than an 'o', but I can't find a word that sounds like 'beg' but means something appropriate.