Runes are used phonetically, so most of the time you should shorten double-letters to single-letters ("Hello" would become "helo"). All the appropriate runes are bound to the appropriate keys, so you can type freely without worrying about which rune you're using. However, a few runes which represent diphthongs which are unused in Modern English are bound to the SHIFT-number row. They are as follows: !-th, @-eo, #-ng, $-ɶ, %-æ, ^-ia/io, &-ea, *-kk. (-st. Additionally, in Old English, there are two types of "g"s, a soft "g" (which is bound to the "g" key), as in "sage", and a hard "g" (which is bound to the ")" key), as in "saga".
Keys 1-7 also include the different Roman numerals (I, V, X, L, C, D, M), which can be combined to make up a number (from what I can tell, the Anglo-Saxons probably used Roman numerals or tally marks - most likely the former).
Just in case anybody wanted a small, serifed, pixel-sharp font with personality and figure (old-style) numerals, I whipped this up... then overachieved, perhaps. It has full Latin-1 and Latin Extended-A support, extended punctuation, most Greek, and as much Cyrillic as I could justify working on. It also has some Roman numerals, many arrows, and a few other random things.
If anyone out there actually wishes to use this for setting anything with Greek or Cyrillic alphabets, please let me know if I've made any terrible errors or if more characters are desired. I know better than to trust my typographical sense for alphabets I don't use in an actual language context!