Thanks Jonathan for the additional comments and feedback. More than 1 person saying the same thing is always encouraging!
I am pretty much committed down the existing gantry route because I already have the ballscrews in hand and can't afford to buy anymore at the moment. My earliests thoughts on this was a metal version of the twin ballscrew- belt drive Solsylva design. I accept that the machine may have some limitations with aluminium milling but as this is a tertiary requirement, then I can live with that compromise for now. Wood, GRP, Plastic and CFRP are the priority at this time, hence the size of the machine in the Y axis. I am looking to source aluminium toolplate (6082 T6) and have found a reasonably priced source in Milton Keynes (MetalFast) but that was awhile ago so I will need to recheck.

Kind Regards
Mike