short, long adjective, adverb for two consecutive words

Question

In Nicholas J. Brown's book, The New Penguin Russian Course - A Complete Course for Beginners (1996), there is an exercise (27.5 if it matters) containing a sentence;

Девяносто пять процентов тех, кто участвовал в опросе, назвали Кларка Гейбла единственно возможным Реттом Батлером.

Questions:

I. I assume that the last four words are in instrumental case because it is like a profession, to be this Ретт Батлер. (Question 1)

As it is written...

II. I believe that the two words I am inquiring about , единственно возможным (Реттом)..., are an adverb, followed by a long-form adjective used attributively. (Question 2)

I don't see a 'linking verb' so I assume that the adjective 'possible' is used attributively. (Question 3)

I can see that the adverb 'only' is modifying the following long-form adjective 'possible', but what would it mean if the adverb was replaced by a short-form adjective (I think two consecutive adjectives used attributively, maybe even predicatively, require the first adjective to be short-form. (Question 4)), therefore modifying the same noun 'possible' modifies, as in the following?

единственен возможным (Реттом Батлером)...

Since short-form adjectives are only used predicatively, would this be valid as there seemingly is no linking verb? (Question 5)

If I wrote it from scratch...

If I was going to make the sentence from scratch, can't both consecutive words единственно возможным actually be constructed attributively, as long-form adjectives (Question 6) and written as

_единственным возможным (Реттом Батлером)..._, 

as they both precede the noun (Ретт(ом) Батлер(ом)) they modify? (Question 7)

By this site, when to use the short form of an adjective?, I understand the temporal/permanence features of the long and short adjectives, and so there may be more permanence with 'only' in this case. (Question 8)

Answer 1

The Nominative case of the phrase under consideration is

единственно возможный Ретт Батлер

But the verb называть requires the following cases.

Называть кого-то/что-то (Accusative) кем-то/чем-то (Instrumental).

So, единственно is an adverb used as a particle, and единственно возможный/-ая/-ое is a set phrase. The word единственно has no declension.

The phrase единственно возможный is an attribute.

There are no short forms of anything in this sentence.

But still, we can discuss them. We can't replace единственно with единственен for two reasons.

First, we don't generally use this strange word. :) It sounds outdated and hard to say. And hard even to imagine where to be used betted than the full form единственный.

Second, in this phrase the notional characteristic is возможный, and единственно/единственный is a modifying word for it. In such cases it is pretty weird to use a short adjective. Besides, we can't shorten a particle.

However, it is possible to shorten the notional adjective, but usage of a shortened adjective requires some changes in the word order. A shortened adjective is not used attributively. The only variant possible is

Они считали, что такой вариант единственно возможен.

If we wanted to modify the phrase discussed, it could be единственный Ретт Батлер, который нам нравится, for example. Then, we could compose the phrase

"мы назвали Кларка Гейбла единственным Реттом Батлером, который нам нравится".