I like the idea of this a lot!
Would you consider releasing a version with different keyboard controls? On the Spectrum, traditionally, Q and A are Up and Down, and O and P are Left and Right.
You could also make a version with arrow keys for movement.
Or add in the redefine keys option that MPAGD has.
The controls are one of the most important parts of a game. Setting them up to be comfortable to use will help a lot!
Hope that helps, and sorry for the unsolicited advice!