Will PrusaPrint work with an external raspberry pi on a prusa i3 MK3

What is the problem?

What did you already try to solve it?

Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...)

For it's practically is OctoPrint, it should run (much better) on a full size RapsPi

Yes Octoprint does, but does PrusaPrint - or does it expect the internal interface of a built in Pi Zero?

As far as I know it's just a custom build of OctoPi and should work fine with any RPi.

But since it's Prusa Research's image, I suggest you ask Prusa Research on how they customized it and if it works, they will now best.

prusa print, is really just octoprint with the printer profile installed. you can Google those settings and just use default octoprint.
to attach the pins to the printer with the headers and not USB you will need to connect all pins MINUS the 5 volt pin, but you must have the ground pin (reference) connected. see prusa's forum about this.
I have been running it like this since the first day. with no problems. in fact it's the only way I run my printer.
I may make a blog on this of how I made my own header cable and how i set it up.

Correction: PrusaPrint is really just OctoPi with some preconfiguration and default OctoPrint. Said preconfiguration includes the printer profile. You can Google these things and the just use default OctoPi with default OctoPrint.