Re:  … honum þótti þat líkast í hýbýlum Guðmundr skáld og hundr sá, er Rósta hét …

>> … that seemed to him most-likely[that] Guðmundr [the] scaldic-poet and that dog, which was-called Rósta [were] in [the] homestead …

>… he thought Guðmund [the] skald most like [amongst those] in [the] household the dog that was called Rósta [‘brawl, riot, tumult’] ...

To me <líkast> looks neut nom sg, so therefore it must be agreeing with <þat> rather than <Guðmundr>.

You’re right; I clearly wasn’t paying enough attention there.  On further consideration I’m inclined to think that the sense here is probably ‘most fit for, most suited to’ (the current situation), implicitly likening Guðmund to Rósta.

Brian