I looked up some things in my Proto-Norse
grammar book and it seems that every grammatical
ending that has 'r' in Old Icelandic has an 'R' in
Proto-Norse.

My book (Frumnorræn málfræði) gives the genitive
singular feminine of the adjective for 'blind' as:

*blindeRoR

I suppose that would in runic Swedish be:

*blindRaR

So there is no guarantee that 'R' marks the end
of a word.

- - -

DeepStream's solution of the puzzle was to read
a u-rune with its name; 'úrr' = 'cow'.

Góð eR <úrr> undiR hánum auk yfiR hánum.

"There is a good cow under him and over him."

An amusing theory but the practice of using
runes to represent their names is very rare
in runic inscriptions (common in mss).

Kveðja,
Haukur