Revised the schematic and board layout. Shift register->SID connections now inverted so Q7->D0 and Q0->D7. Requires a change to the SPI initialisation to be compatible but the board layout is a lot neater. Now only a single layer, no extra wires required. Make the power lines a lot thicker - I believe this is the thing to do. Added additional 5v power out header to power external Arduino.
Merge branch 'master' of github.com:CharlotteGore/MOS6581