It'll quite likely run too fast with a turbo board

- I commented out the "wait for vertical blank" to make it run a bit faster (albeit very flickery) on the standard Electron.
It'd probably be quite easy to put something together that runs full speed with a turbo board (maybe even the normal BBC version, if the Electron incompatibility bug is fixed), though I don't have the hardware to try it myself.
There's certainly scope to make a better Electron port too if anyone wanted to spend the time - either by keeping it in Mode 2 and using smaller sprites, or by moving everything to Mode 5.