If you don't want to start completely from scratch, may I recommend you take a look at the VideoBrain? https://en.wikipedia.org/wiki/VideoBrain_Family_Computer (only language ever available for it was APL/S -- "structured" APL.)

Also, the "Decker" Hypercard-alike has a K-inspired language that is pretty nice. (Yes, much more modern, but still feels a bit like something "of that era".)