I considered many different ideas:-
1) A full sheet of perspex on the front of my enclosure. Great finish but expensive and difficult to seal as fully transparent.
2) A small piece of perspex over a cut hole in the enclosure. Cheaper but not so nice finish, showing the full LCD through and any rough enclosure cutting.
3) Looking for access to a laser cutter to make a profiled perspex window that sits through the enclosure hole to sit flush with surface. Difficult tolerances and no depth control with a laser.
4) Asking a local workshop to make a profiled perspex window on CNC milling machines. Cost more than using a full perspex sheet.
So, eventually I tried something else and ended up with what I think is a nice professional finish that is easy to do, cheap, and results in an iPhone type black glass frame style, with a clear window exactly the right size to show the display properly. It can also be easily adapted to any other type or size of display.