I had a similar role not that long ago, and still fucked it up intonatially speaking. Fact is, it's impossible to know the accent, unless you're there soaking it in.

4.5/5 for faking it truly well. Maybe we both need to micro-dose and watch more mid-late 20th century movies/tv shows.... or, just 'be here now' or wherever the 'here' and now is. The best 'artists' I've seen, researched and nailed the lines before committing.

If nothing else, I would recommend you to others on this site for a salient and heartfelt narrative.