Steve White has developed a wonderful application for a Raspberry Pi 3: Pi1541
Pi1541 is a cycle-exact emulator for the 1541 disk drive. Have a look-see. If you want to try this out, you’ll need some soldering skills to make the cable that attaches the C64 IEC bus to the Pi’s GPIO.
If you’ve already got Gideon’s 1541 Ultimate, there’s not much call for the Pi1541, but a Pi costs you less and you might have fun with the DIY aspect of putting it together. (The 1541 Ultimate still can’t be beat, especially considering the freezer functions you get with it.)
Also, I haven’t tried the Pi1541 yet, but I suspect the SD2IEC output from GB Organizer would work well with it. Steve’s Pi1541 seems to work much like an SD2IEC on the computer-side.
Here’s one of Steve’s videos on the project: