Got the Perspex back from the waterjet cutters today and made a start on drilling and boring the holes. Due to the odd shape I had to do some lateral thinking and creative positioning of a number of parallels and the jaws of the ARC vesatile vice to get the workpiece within the working envelope of both the mill and DRO. Final result is shown below with the wooden pattern held to check out the positioning.
Once that checked out OK, I placed the cut perspex in its stead and centred up on the top (left) bearing recess. Using that position as the reference point I changed the DRO readings to coincide with the coordinates on the drawing. I'm happy to say everything is working out well.
I'll have a go at the other "walls" tomorrow.
By the way, I butchered an old digital cakiper as per Readers Tips in MEW 292 to obtain a couple of thin parallels, visible in the second photo and they work brilliantly! Good tip!
John