The original article is by Leo Brodie. I bought his book Starting FORTH (which is now available online[1]) shortly after reading a 1980 Byte Magazine article on FORTH.
It's not hard to implement FORTH. I found that R. G. Loeliger's book[2] Threaded Interpretive Languages: Their Design and Implementation allowed me to easily build my own FORTH inspired system.
[1] https://www.forth.com/starting-forth/
[2] https://www.amazon.com/Threaded-Interpretive-Languages-Desig...
https://www.amazon.com/Threaded-Interpretive-Languages-Desig...