The Watchtower Society translates John 8:58 as “I have been” instead of “I am” for the Greek EGO EIMI in their New World Translation (NWT)
The reaction of the Jews gives us a good indication of how THEY understood Jesus with the emphasis on THEY! Jesus wasn’t narrating here nor was he debating. He was making a definite statement which is why the Jews wanted to kill him. THEY understood him as committing the unpardonable sin of blasphemy.
As you already know it is important in interpretation to understand it according to how the hearers at the time of writing understood it and not what we think it should mean. As much as we would like to we cannot make something fit our theology just because we think it should.
One of the sad things about the translation by the Watchtower translation committee is that they did not translate their bible as they said they would in their Forward. They said in their Forward that they translated word-for-word where possible and gave no paraphrase of scripture (a paraphrase is using a phrase etc to explain the word rather than give one word for the Greek).
In John 8:58 they could have given a word-for-word without altering the text but they chose not to. When you read their footnote explanation in their Interlinear you can see clearly that they have done this to fit their own theology regardless of what the text says.
Their footnote regarding this that has proved most interesting.
For example they have given the tense as:
PERFECT INDICATIVE TENSE in their 1950 translation PERFECT TENSE INDICATIVE in their 1961 translation PERFECT TENSE in their 1970 translation PERFECT INDICATIVE in their 1985 translation
On all four tries they did not get the correct tense for “I have been” which they could have obtained from a USA 5th Grade Primary level textbook - “I have been” is PRESENT PERFECT TENSE INDICATIVE.
Greek Scholars world-wide have been amazed that they could take EGO EIMI (present indicative) and make it “I have been” (present perfect indicative)!!??
Whether it suits your theology or not - EGO EIMI is translated by the English I AM!
They were getting close though when they described the action of EIMI as action begun in the past and still in progress. This ties in with the description of Jesus in Hebrews 13:8 - Jesus Christ is the same YESTERDAY, TODAY & FOREVER! That Hebraism (colloquial expression) is a way of saying that Jesus is Eternal. Only God is Eternal - the same Yesterday, Today and Forever - who IS, who WAS and is to COME.