well the inner edges are only used to reference the tailstock. I haven't checked them yet, thats my next task.

I have a box of 150mm x 3mm parallels and a pair of 240mmx20x35 parallels

I measured up the bed and the table of the mill... I could get the bed on the mill if I sat it on some 4" high blocks and shimmed it to get the top level, the legs would protrude out over the ends. I could reference a test bar held between centres to get the bed parallel with the table.. that would allow me to determine which faces are also paralell. I was thinking that if I was then to mount a 2" grinding wheel in a collet in the mill I could grind the rear surface parallel to the test bar, setting the head low enough to use minimal quill travel... then once I had done that I could reference everything else from there...

I am less sure about how to deal with the top surfaces of the bed... i certainly wouldnt want to use a facemill on them - the Z accuracy of the mill isnt good enough. If i mounted the bed on its side and used the ends to reference off that would tell me how far out the bed was. I dont have a long enough straightedge to do it otherwise. I wonder if the grinding wheel in the collet would work here tho as the quill travel is 110mm approx and the bed is 103mm wide.

I dont know anyone locally who could do this. I had a spindle reground locally but that cost me £40... this would be much more than that I reckon...