Guur might be the modern Welsh Gŵr ("man"; "husband"). Griffen* (p.85), apparently unaware of this use (the other use appears to be in Guurci, see below), discusses a hypothetical word *Guur (where the * denotes hypothetical, and the underline a "glide"), which he suggests is an early (Brythonic to Old Welsh transition? ~8th C.) form of Gŵr. He suggests that while Gur appears in the oldest (text 'B') copy of the Gododdin, (see Other Works) the uu combination never did because the way u was pronounced would have rendered it pointless. Koch*, seems to argue otherwise, but also suggests Gur scans as Gwwr in early Welsh poetry.
Guor, which is the form found in some of the manuscripts (See Note on alternative Variants) is a common component in Old Welsh compound names*, suggesting Helic is a name rather than, for example "Willow". As a name prefix it is found in the oldest Welsh Genealogies (see Other Works), particularly those associated with Manuscript A (note, however, that in this manuscript the wonder has Guur not Guor, and the attached Annales Cambriae (see Other Works) also contains the name Guurci rather than Guorci [at ~577]).
Ford* pulls together the genealogies for Cynedda Wledig which shows nicely the use of Guor. While he suggests it is a mnemonic used with name repetition (so guor-name and name are the same individual) it could equally be being used as an honorific (cp. gwrð "manly"*; Koch's* hypothesised Brythonic *guorgou "best", leading to today's gorau; and guron/(posibly also guoron) "hero" leading to today's gwron*) or to distinguish a predecessor in a tradition of name repetition (one could note the use of cu/gu "beloved/kind/dear" in South Wales in the terms for grandparents tad-cu "Dear father", mam-gu "Dear mother", as a somewhat stretched analogy).
With this in mind, it would seem Guur could be a dictation/transcription of pretty much any of the above, or, indeed, something entirely different - for example, given the widespread use of springs as boundary markers noted by Jones* (who speculates this may be particually true in the case of well-names containing pen "head" followed by a name) it could relate through mis-transcription to Cwr "outer limit of an area", making it something like "the well-pool at the end of Helig's land". We await Vol.10 of Dumville's The Historia Brittonum (see Translations) which he notes* will contain a full study by K.H.Jackson of the Welsh language forms.