I'd forgotten about those round way things. They always strike me as being a prime candidate for resonating and rubbish finish, and that's before you consider the lack of adjustment once things wear a bit.

Ideally I'm looking for something with linear guides, and I was wondering if it would be more cost effective to buy something already with them, rather than convert something.
At the moment my primitive plans are based around a Clarke CL430, as it's about the size of machine I'm looking for, and I happen to have a CL500M (same machine, but with a milling head) so I know it has a nice flat topped dovetail way that would be near perfect for bolting linear guides to. Most manufacturers seem to be using either single or double V ways on this size of machine now, which is good for a manual machine, but not for when you want something you can butcher to eliminate play as best as possible!