Peter,
If you are doing a new pcb for the Mk2 may I suggest that you keep to the original overall dimensions of the board? Hopefully the extra bits can be squeezed in (I don't recall the original to be particularly densely laid out) and this will enable anyone who has a Mk1 to keep the same enclosure and mounting should they wish to upgrade to a Mk2.
Best wishes to you and many thanks to both Ian and yourself for a great little piece of kit.
Steve.
PS A bit more spacing on some of the transistor pads and (I seem to recall...) the audio input pads would be nice too