Sweet, thanks! Well, my design has a rectangular hole cut out for fitting the PCB in of 124.21 x 349 mm, so that should be fine (I'm not looking for measurements of that sort of accuracy, it's just I've been working in inches since the standard gap between keys is 0.75 x 0.75 inches).
The gap between the function row and the alphanumeric section is already the same as on the filco/phantom (took the distances from the phantom mounting plate CAD).
Same with the gap between the alphanumeric section and ins, home etc.
Bit worried about those extra holes on the PCB though. I haven't accounted for those. I've asked bpiphany for the positions of the holes on the Phantom PCB though. I guess the best way of making bits on the case to fit into them would be to fit hex bolts into the bottom piece of perspex.