It's a naive question : I can't decide what's the value of "ġe" in Old English :
either it's a digraph to be read [j], hence "ġeong" = [joŋɡ] (or [juŋɡ] ? as stated here). Such digraphs exist in French (e.g. the first name "Georges"=[ʒɔʁʒ], not [geɔʁge]). It seems to me that this record reads the line #13 "ġeong in ġeardum..." more or less this way : [joŋɡ in jardum], not [jeo̯ŋɡ in jæa̯rdum] as it would have to be said with the diphthongs "eo" and "ea". But if "ġe" stands for [j], what about a word like ġēotan ("to pour") ?
either it's simply "ġ" followed by the vowel [e], leading e.g. to read a diphthong in the word "ġeong" = [jeo̯ŋɡ]. This interpretation would fit with the following extract from Don Ringe's The development of Old English, p.29 :
"PGmc *jungaz 'young" (Goth. juggs) > ON ungr, OE iung ~ ġeong", showing that both forms (without/with diphthongaison) existed. Did such a diphthongaison occur in the course of the phonological history of English ? I can't find any evidence of it.
The only book I have (A guide to Old English, 6th edition, pp 14-15) only recalls that the diphthongs "eo" and "ēo" exist in Old English and that "[b]efore e and i, [...] g is usually pronounced like [...] y in MnE 'yet'".