I've been asked in a PM to show some pictures of my retrofit. It seems like a good time, but my wife has lent the camera to someone, so these are taken with a phone - I'll try and get some better ones later.
Pitcture 1 shows the front, all standard looking here, as you can't see the new steppers under the covers. Original spindle motor. Aluminium swarf in evidence, although I've found cast iron, brass and steel perfectly OK to cut.
Picture 2 shows round the back - I need to tidy up the loose cables, but it's all working. You'll see I have re-used the emco circuit board holders, but none of the original electronics remains. The left hand one just tidies up the VFD for the spindle. This is a Mitsubishi S500 that I got second-hand on ebay. The middle one holds four Gecko drives, mounted on an aluminium plate, with outputs wired to the original sockets, so the steppers can be pugged in. The right-hand holder supports the breakout board, a PMDX with a sub-board to control the spindle VFD. Again this is wired to the sockets on the emco plate, to permit easy unplugging. The breakout board supports two parallel ports, I don't need any extra outputs, but I'm using the inputs for an MPG and switches to control which axis is jogged, and the jog speed. I suspect If I did this again, I'd use an all in one Gecko G540. Not that I'm unhappy with what I've got, it would just make it easier, that's all. What you can't see to the left of the shot is the power supply section - this is all original and supplies the 240V for the VFD and the breakout board, together with 24V for the Geckos. I know they can take more volts, but I'm quite happy with the speed I'm getting from this set up - it's only a small machine.
Picture 3 shows the new Y-axis stepper. You can see how it's mounted onto the original motor support plate. This was very easy: it's rotated anti-clockwise slighly from the original motor position, and new mounting holes drilled and tapped. You can see one of the original holes in the plate to the left of the lowest mounting screw on the motor. As noted earlier in this thread, in the UK I could get motors with a 6mm shaft, so the toothed pulley was an easy swap from the old motors. Each pulley was shortened slightly (at the boss end) and cross-drilled through pulley and shaft, and secured with the original roll-pins. All the motors were fitted in this way. Cables are new, shielded. You can see that the motor had shafts both sides - I've sawn off the spare. Right at the top of the photo, you may be able to see the axis limit switch, this is as original. All three axes limits are now wired in series and are also acting as home switches. The encoder switches have been removed.
I'm running Mach3 on an old PC. I'm 100% happy with this and it has the advantage of being the same program as a friend uses, so we can help each other out. And I'm more familiar with Windows than Linux. If I did it again, I'd have a serious look at EMC2.