This is great work lets hope you can get your gear and progress this - I will help where I can of course as it has been one of my goals. Since I was unable to share my copy of the article due to it being a licensed reprint from the Museum someone has scanned the issue to archive.org so you can see it here:
https://archive.org/details/Personal...ge/62/mode/2up
One thought it might be nice to support an 8K ROM though to allow Karen O's Page 2 addon on-board Assembler.
https://www.vintage-radio.net/forum/...d.php?t=168405
I have been toying with an i2c interface for something like a 24LC256 on small removable cards so with some code squeezed into the Page 2 ROM you would have a relatively cheap mass storage device that should be able to be used fairly easily.