After a lot of thought, I decided to replace the Mini-DIN-8 joystick connectors with standard DB-9's. This might be a controversial decision, but I really think there is no point in keeping that odd connector since it's very hard to find a joystick that is using it. We are not making a replacement board for damaged C16s but rather trying to bring the C16 into the future so there's no reason to strive for compatibility with a dead standard, if a standard it ever was!

I put the +5V power rail on pin 7 of the DB-9 port as the Amiga and C64 do, but I also left the option to connect it to pin 5 as required by Sega Mega Drive controllers. You will have to close a jumper to do so (JP9/10) as this can be dangerous in certain cases. Don't do it, unless you know what you're doing.

Replacing the joystick connectors forced me to replace the power switch too, as the original one is wider and would clash into the DB-9 ports. This is actually good news though, since the original one is nowhere to be found and the C64 switch is a perfect substitute both electrically and mechanically. The exact original C64 switch might not be easy to find either but there are a few alternatives. Let me quote this post by Lemon64 Forum user Skyfox:

• Salecom T80-R (R8011L/R8012L), for sale on RetroTech and eBay; near perfect match (I just bought some).
• Sky KS-SP-222A, for sale on eBay (may be listed as KSSP-222A).
• C&K 7201J50V5QE2 (silver contacts) or -SE2 (silver with tin contacts); these would be a special order since nobody stocks them. Turns out, the gold contacts are not rated for the amperage used by the C64 so couldn't be used. [7201=DPDT switch, J50=the correct cap for C64, V5=the thin pin support mounts, Q for silver or S for silver with tin, E=epoxy sealed, 2=black cap. Info based on datasheets]
• C&K E201J50V5QE2 or -SE2 with the same part number coding used above. These would also be a special order as nobody stocks the switches with the thin pin support mounts. Everything anybody stocks has thicker standoff brackets on the bottom that would misalign the switch cap with the hole on the C64 or 1541-II or 1581.
• NKK M2022TXW41-FA or -DA [M20=switch series, 2=DPDT, 2=on/on, TX=narrow frame for small actuator, W=silver contacts, 41=right angle vertical mounting, F=.450" wide rocker {rocker model # AT4150} (D for .365" wide rocker, but it's .169" {4.3mm} taller and might not fit the opening on the side of the computer or disk drive case), A=black cap. Info based on datasheet.] NOTE: This switch may have the raised bracket on the bottom rather than the thin mounting pins. If it's the bracket, that would have to be cut off before mounting on the C64. If anybody has bought one of these switches, please let us know.

As you can imagine, I placed the joystick ports and the switch exactly the way they are on a C64. This means that it should be possible to design a replacement side bracket, possibly 3D-printable, in order to still be able to put the board in an original breadboard case while still keeping things clean. There are some designs on Thingiverse already that could probably be modified for the purpose but I am totally incapable of doing any 3D modeling, so any help in this regard will be welcome.

To tell the truth, the replacement of these connectors also had a downside, as it forced me to remove the reset button. I really didn't want to do this but there was just no place it could be fit into. I replaced it with a pin header though (JP11), so that a switch can still be connected and placed somewhere, or left hanging through the cartridge slot (Please do NOT drill any holes in your case!). Maybe it could be that could be fit in the top section of the replacement bracket, where there seems to be some space available. If you design one, please keep this into consideration.