>> "I do not like
>> green eggs and ham.
>> I do not like them,
>> Sam-I-am."
>
> 'græn' seems like a good guess anyway, unless I'm hugely confused,
> since neuter plural = feminine singular...

Yes, that fact makes this a bit less problematic. It's actually line three
that I'm really worried about - want to have a crack at it?

>> What you can say is:
>>
>> 4.1 Ég er með nytsama fætur og augu.
>
> I might be making a false analogy here, but this reminds me of those
> constructions where the verb is singular but has two subjects.
>
> brenn fold ok fen (Hervarar saga)
>
> ok var þar Ásgautr ok Þórólfr (Laxdoela saga)
>
> ok verðr prís ok gleði mikil í höllinni (Ála-Flekks saga)
>
> en hann ok ek skal veita yðr fullan styrk til allrar framkvæmðar
> (Fagrskinna).
>
> Does that still happen in Modern Icelandic?

A very good analogy in my opinion! Using my own idiolect the first and
third of your examples seem fine but the second and fourth less so. I
think in cases like this the singular sometimes feels more natural than
the plural even when the plural might be pedantically correct. This may
especially be the case when we're not speaking of people.

Kveðjur,
Haukur