I was just re-reading this as the time (aka, the money) has finally come to get the job done.
I will get a quote to have the cross slide and gib reground at the same time/prior.
I will also mention I want it to turn ever so slightly concave, I will pull some Schlesinger specs up.
I will also quiz further (If required) about the refitting on my headstock because I have a feeling it does sit on both Vee's and so will be very sensitive to any change in the centre to centre.
The company doing the work is Birmingham Machine Tool Services, if anyone has any recommendations let me know.
Thanks again to everyone for sharing their experiences and knowledge.