8 BC547[/a/b/c] transistors
1 220ohm resistor
9 10kohm resistors
1 1N4148 diode
1 6n137 optocoupler
1 5-pin din socket such as the Hirschmann MAB5SH, though most should fit
1 24-pin wide dip socket (optional but advised)
1 4 way DIP switch
1 casing such as the Terrington Components MDRX2KD09
5 10mm m3 bolts, washers and nuts. Three for the mod casing and two for the socket on the DR-110
1 2x5 IDC socket with mounting ears, such as https://www.ebay.com/itm/172302042862
1 2x5 right angle female PCB header
1 10-way 12.7mm pitch ribbon cable (less than 200mm)
1 PCB
1 Arduino Pro Mini