Hi there, Andrew,
Should you decide to home-brew a 19" rack, I have an Imhof catalogue somewhere in my filing 'system' that might have any dimensions you need.
My last experience with 19" hardware was complicated by ensuring consistency between the mounting screws and the cage nut - the options were 0 BA, ¼" BSF or M6. That's the recent 19"-lite, the traditional was 0 BA tapped holes in good old solid mild steel angle. Imhof must have had a standing order with the tap manufacturers!