Are you saying that you're going to imagine the cube, and then instead of imagining colors on it, you'll put numbers for each target, so that as you solve, you can go look around the cube for the next number?
It doesn't sound like the best system. It doesn't seem like it would be fast and it would be really easy to misplace a number because, at least for me, they don't really have as much meaning as words.
But this does appear to be a visual system. The only other type of system that I know of is audio, and this clearly isn't audio.
iirc Marcin Kowalczyk didn't use a 'normal' letter system. He used numbers in place of letters, and 'randomly' assigned meaning/words to the numbers, and then put the words in rooms like how most people memo blind.
But also, I would strongly recommend staying with a Speffz + Rooms memo system as it's really good. It's definitely a pain to learn in the beginner, but after a few hundred solves, it gets a lot easier and more comfortable, like anything. Also, because most people use it, you can always ask questions and there will be answers.
