Well today I needed to use the drill press since my mill was setup up with another project.
I had made the aforementioned support columns so I quickly decided to level the table. Whilst doing this, I noted some other rather "interesting" readings on my Dial indicator.
The result of which was that I took the table off and checked it on my granite surface plate.
Yep you all guessed it, not only does the stupid thing flex, it's also warped!

I gather the casting didn't undergo any stress reliving and this was the result.
The surface is so bad that I could probably have done better by offhand skimming the thing with an angle grinder fitted with an abrasive disc.
This leaves me with a few options.
Take the thing to a machine shop and get it resurfaced. Not even sure where to start looking around here.
Make a sub-table of some kind and level it with shims
Level a cheap X Y Vice with shims
Curse the thing and take it to the rifle range where at least it would see some good use as a "gong"
Bite the bullet and just make sparky's table.