Looks good mate. are you happier with this as well?

Whilst myself and others could carry on making suggestions to tweek if further I think you have got to the point of a build-able machine, without going into calcs you have gone as far as you can.

The only point I would make and it is minor and that is that you might need to add additional support to the top of the X axis bearings to stop them opening up due to the weight of gantry, placing the rails and bearings on their side will improve load capacity but some of the cheaper bearing holders can give and open up the bearing.

I apologise for misleading you with the table distance as I presumed you meant with the z axis at the top of its travel. I see from your drawing you are talking about it a full extension.

I have seen this design before and dismissed it as being to difficult to build
yep thats one of the reasons I abandoned it, cheap but difficult to build. I was mainly showing it to you for the rail orientation.

The welding part is easy but to make it accurate would mean a lot of shimming, as you know welding one side of the metal joint twists the steel one way and when you weld the other side of the joint it will pull it back again
The design was actually for Ali sections and they would have been bonded with epoxy and riveted for good measure. that way no distortion due to welding.

I never got around to building it so no photos I'm afraid.