I have been in the middle of the same ( Hurco KM3 ) conversion for some time.
I am overbuilding / over complicating this build because I have machine paranoia. I do not believe that any machine motion should be controllable via an HID ( keyboard or mouse ) so all jog commands will be hard wired with appropriate switches into GPIO.
I am using a HP DC7700 mATX with a with a 5125/7i77 and a 7i74 on the 5i25's 2nd port. I have several of the 7i77 plugs wired up and am dealing with issues of too many differing control voltages. The 7i74 allows me to use multiple SSerial cards for more I/O for the panel and other options.
I removed the Hurco OEM Intel Multibus card cage and OEM control power supply. The ServoMate uses 120VAC 1ph that it gets from the OEM stepdown/isolation transformer. I have a Teco FM-50 VFD to drive the spindle motor and I will add a run capacitor or 1/4hp VFD for the coolant pump so the machine can run on 240VAC 1ph.
I do not intend to control spindle speed with the VFD. I will use it to ramp up to speed 2.5 seconds to 60Hz and likewise 2.5 seconds to stop. I will use the Vari-drive to control speed for now to provide best Hp/torque from the motor running at its data plate rpm.
I have (lost at present) the VFD breaking resistor which will allow for harder spindle breaking in the future. Since I read that G84 has finally been supported (v2.8 or later) I will be able to tap using the U200 tension/compression tapping heads I have for the Hurco.
I am waiting for a tapered gib for my manual mill that was ordered a few weeks ago to get that machine running again so I can complete the chassis parts and get things all mounted up. Being impatient I used my 3D printer to make a partial gib since I could not print a 15" part. Was a partial mistake. I used AL spacers at each end to center the gib - but as I used the machine it pulled the gib into the taper and wedged it in there but good. The AL end spacers just deformed the plastic more, increasing the wedge effect.
I have made up several spread sheets which document where a signal wire is sourced on the Hurco (using OEM wiring diagrams) and which terminal connector it is connected to on the Mesa boards.
I have 24VDC/6A and a 5VDC/4A power supplies - how ever after reading many of Gene's rants I am wondering how clean these power supplies will be. I don't have a scope at present, and no budget.
While I have done an install on a laptop HDD with v2.8pre I have not begun any config. I have a remote pendant that I may use exclusively for jog functions until the machine is running well enough to cut out a proper control panel.
I have yet to tackle a good hardware E-Stop Chain. Also the OEM Icecube relay panel the Hurco used is running 120VAC control voltages to drive air valve solenoids and Siemens contractors for spindle and coolant. I will have to work with some of these, but have not gotten to that point.
Part of the OEM Hurco E-Stop signal went along with the keyboard signals which totally voids its re-use.