I have been translating Aischylos' Eumenides, and I think I have come across an instance where the aorist middle participle is used with "exein" to form a periphrastic construction; however, Smyth's Grammar seems to indicate that this construction is only used when the aorist participle is active or deponent. Look at these lines from the Eumenides:
I cannot find any other way of translating ἔχειν; Hence, I translated these lines, " It is at hand for me to behold that the navel of the earth has born a terrible curse of blood. Is this a periphrastic construction, and is my translation of πάρεστι correct?
When translating I let myself read the original many times, calmly, pausing and reading again, pausing, reading... until my mind starts to approach the meaning before translation.
Paresti, by itself means that something or someone is, and is here, beside us. The placement (order) of the words is not accidental. Paresti is placed near what Aeschylus wants our attention to focus. A few lines above there is another paresti opening two lines symmetrical with those you translate. This way omphalos is compared with doomsman and stressed even more as monstrous.
In your translation I think omphalos is placed too far away from paresti and loses strength. Another possible translation would be, “Here it is!”, or “Behold!” “The earth’s navel” [= the very navel of the earth, the spring of life, what worst could ever happen!? – this is why it is placed at the start of the sentence, and then:] “before my eyes in bloody grim foul-mouthed Guilt.”
If you haven’t done it already, read also Elpenor’s second lesson (both pages), (skip grammatical information you may know) where just a few lines of Homer are translated; I think it will help.
In the first place, there is no grammar. Language comes first, people just speak, and grammar tries to describe – if and when it tries to describe. Don’t subjugate language to grammar, the opposite is true; grammar is just an artificial aid and does not describe language perfectly.
In any case, if agos is connected with aromenon, why can’t agos be also connected with ehein? It is usual for a word to have simultaneously many functions in a sentence. Note also that you translate paresti as an impersonal expression, in which case is almost a synonym to exesti (=it is possible, I can) and is followed by an infinitive as its subject.
Without excluding the possibility of your translation, I translate it as I said above, following the strength of the scene, which does not permit impersonal expressions (e.g. [an example not far away of the very sentence we translate] when I see a dead body, I don’t say “It is possible for me to see a dead body”, etc, I say “Here is a dead body!”), and is almost a literal translation (even in the order of words) except for prosdrakein, which I rendered freely “before my eyes” meaning (at least this is what I intended) visible enough to grasp it.