Is there a difference between an Elder Futhark ending in O-D or one ending in D-O? I've found a few articles claiming that D-O is older, but I see O-D quite often, too.
The single oldest attested full rune-row is probably the one on the Kylver stone, estimated to be from around 400 A.D. on the basis of the grave it was found near (although it isn’t beyond a shadow of a doubt that the stone and the grave go together, it’s still likely the oldest). This stone has the futhark ending do:
However on bracteates the order of the last two runes is reversed. Below are the Grumpan-C and Vadstena-C bracteates, respectively (there is also the Motala-C bracteate, but it was struck from the same die as Vadstena). On Vadstena the d rune is covered but it’s clear where it is meant to be.
Images from Hauck, Karl et al. 1986. Die Goldbrakteaten der Völkerwanderungszeit. vol. 2.2. Munich: Wilhelm Fink Verlag, pages 47 and 157 respectively.
I don’t know the Anglo-Saxon corpus very well but George Hickes’ edition of the rune poem has od like the bracteates:
(https://commons.wikimedia.org/wiki/File:Rune_poem_Hickes_1705.png)
…while Codex Sangallensis 878 has do:
For further reading I’d suggest:
Looijenga, Tineke. 2003. Texts & Contexts of the Oldest Runic Inscriptions. The Northern World, 4. Brill: Leiden.
Senra Silva, Inmaculada. 2003. The Significance of The Rune-Names: Evidence from the Anglo-Saxon and Nordic Sources. PhD. dissertation, Universidad de Sevilla