A very neat job, Robin. I made something similar a few years ago. My version also has a wooden frame, but the top surface is of 1/8th in. thick aluminium with a central support, then sprayed white with automotive paint. My frame takes prints up to 12" x 10". Over the years I've gradually added markings for the various sizes I print. The strange slightly portrait format is for stereo prints for a Holmes viewer. As you can see, I went to town with the holes! I made a steel flange and welded a piece of pipe to it to give the right angle vacuum connection. The flexi pipe runs under the darkroom bench and up into the loft, where the vacuum cleaner lives and is controlled by a mains switch in the darkroom. As you say, one of the most useful pieces of darkroom kit I've ever made.
Best wishes,
Steve