Well after a bit more rummaging I came across
eDrawing Viewer which I used to use yonks ago.
Out of the apps I've tried this lunchtime this is the winner. While it only lets you view the DWG (you can't edit or draw) it does at least handle Paper Space and Model Space simply and it does have some basic Markup Tools which lets you create dimensions to ensure your DWG has exported at the right scale.
http://www.edrawingsviewer.com/ed/edrawings-mac.htm
AC versions 3.41 to 25 (UKI Full 5005).
Using AC25 5005 UKI FULL
Mac OSX 10.15.7 (19G2021) Mac Pro-2013 32gbRam AMD FirePro D500 3072 MB graphics