So it seems like with the right code (and maybe a ton of future infrastructure for training?) Eliza could have been much more capable back in the day.

The original ELIZA ran on an IBM 7094 mainframe, in the 1960s. That machine had 32K x 36-bit words, and no support for byte operations. It did support 6-bit BCD characters, packed 6 per word, but those were for string operations, and didn't support arithmetic or logical operations.

This means that a directly translated 40 KB Z80 executable might be a tight squeeze on that mainframe, because 40K > 32K, counting words, not bytes. Of course if most of that size is just 2-bit weight data then it might not be so bad.

ELIZA running on later hardware would have been a different story, with the Z80 - released in 1976 - being an example.