i've spent a couple of days beavering away at Blok Copy (since i've finally got myself into a state of mind where coding is possible now) and the game itself is functioning perfectly. A little too well in fact, in the way that i start expecting it to crash and burn hideously at any moment! The presentation is still assuming there's a PETSCII font and isn't doing what it's supposed to but i'll get around to that next.
Thinking about it a bit more, i want to try converting it to the BBC Micro as well; that could put up a bit more of a fight to be honest, there's only 32K of RAM on a stock BBC and the best bitmap mode to use needs 20K just for the display (and a character set in memory will need 4K as well) but there are other options and i need to read up on the hardware a bit more before i make a decision as to which mode to go for. It might end up in four colours if things get desperate! All told, the various versions will need at least four different graphics sets (all laid out in a similar way) and somehow i've got to find a musician willing to do tunes for at least five platforms...!