To do something concrete, we can derive the cardinal numbers of Jamtlandic. I'll use the references
 Hammerdalsmålet, Vidar Reinhammar
 Klövsjöord, Gösta Edlund et al
 Åremålet, Anna-Lena Forsåker
In the table below, H, K and Å will refer to the dialects of Hammerdal, Klövsjö and Åre, respectively, with evidences found in references ,  and , respectively. Furthermore, N will refer to the reconstructed etymology of the (Late) Jamtlandic dialect of Old Norse. (I'll use this site as a source for the reconstructions.) Finally, J will refer to the derived orthography based on the dialectal evidences and the ON etymology.
The first cardinal numbers (in the sense of abstract counting) are given by
H K Å N J
1 [eɪtː] ? [etː] eitt eitt
2 [tʋuː] ? [tʋuː] tvá tvó
3 [tɾiː] ? [tɾiː] þría trí
4 [fyː.yɾ] ? [fyː.yɾ] fjóra fýre
5 [fɛmː] ? [fæmː] femm femm
6 [sɛks] ? [seks] sex seks
7 [ʂʉː] ? [ʂʉː] sjú sjú
8 [ɔ.ɔtː] ? [ɔ.ɔtː] átta átte
9 [ˈniːə] ? [ˈniː.i] níu níe
10 [ˈtʰiːə] ? [ˈtʰiː.i] tíu tíe
Note here that  lacks any references to the lower cardinal numbers, and that the numbers 9 and 10 in the Hammerdal dialect surprisingly aren't apocopated. One would have expect the same as in the Åre dialect. Also note that the Old Norse etymologies tvá, þría, in some dialects (and usually spelled in the literature) þrjá, and fjóra are masculine accusative. This is in contrast with eitt which is neuter (accusative?). Cardinal numbers greater than 4 weren't declined in any way in Old Norse. The final note is that the reconstructed etymologies femm [fɛmː] and sjú [sɪ̯uː] are usually spelled fimm [fɪmː] and sjau [sɪ̯ɒ.ʊ] in the literature on Old Norse. The Old Jamtlandic dialect (like many other ON dialects) probably had femm and sjú, which is the reason I use these as etymologies.
To be continued...