It’s just standard reduction. Whether it’s a stretch or not depends on Guybrush’s particular English accent.
The and is not pronounced like /ænd/ except in emphasis. Even in emphasis we’re talking mainly about the vowel. That /d/ is unlikely to show up. The word is normally pronounced /ən/ or /n/. In some contexts it could be reduced to /ə/ or /∅/ (nothing). Nine-and-twenty happens to be in a good position for both of the latter possibilities.
- /naɪnəntwɛn(t)i/ (nine-n-twenty) is the most obvious form, but people don’t like such repetition much. That’s why it could be easily and frequently reduced to /naɪntwen(t)i/, unlike eight-n-twenty or six-n-twenty. People might even genuinely believe they’re saying nine-n-twenty when they’re actually saying nine-twenty.
- /naɪnətwɛn(t)i/ (nine-uh-twenty) is less likely to be reduced further in principle, but any schwa is at risk of being easily lost in fast or nervous speech.
According to this n-gram, it looks like by the mid-19th century you were probably being formal or even purposefully archaic if you used a phrase like nine-and-twenty, so unfortunately it’s unlikely that we’ll have any natural recordings of the phrase. (Some modern person reading the King James Bible doesn’t count.)
Like MI it’s also movie pirates, but it forgoes on the more obvious anachronisms.