Thanks for all your comments so far. I bought a low cost digital scale from Machine-DRO Ltd at the Midlands Model Engineering Exhibition on Thursday and am still thinking about how best to mount is so any ideas would be welcome.
The Warco Super Major Vario (and similar other makes) has a similar DRO mounted on the head with the reading head inserted into the aluminium plate at the front. Something like this would suit me although I don't want to cut a hole in the plate.
Derek T