Hubert did write an article on his lathe, I believe it was published in ME, but it may have been in EIM. Again, google is your friend. He said in the article that in the final analysis, he thought it cost more to make his lathe than buy one. He did build a beauty though.
The Gingery designs do have a lot of neat ways to build things. Bar steel T slot tables and gibs, for one. However I do have concerns about cast aluminum as a basis for machine tools. It has very poor damping of vibration, being one third the weight of steel/iron, it is also one third the strength and rigidity of iron, and has a very high rate of thermal expansion making it dimensionally unstable if the temp range varies. It does not wear well either, if things are threaded into it frequently or bearing on it. Bushings are needed in both cases if the aluminum casting sees frequent use.
The gauge plate bed is not a bad idea, but I would bolt some heavy bars of cast iron (maybe durabar) to the underside to add rigidity and increase damping if you do it with gauge plate. The epoxy concrete you mention might do a similar job but I don't have much experience with it. I know cast iron is the material of choice in commercial pro grade machine tools hands down, proven over centuries.
If I were building a lathe from scratch I would also use all ball lead screws and purchase antibacklash ball nuts to go with them. These will add quality and accuracy at low relative cost and will decrease fatigue and motor power requirements.
Have you looked around for used industrial lathes rather than building a lathe? A used industrial lathe is a fast way to get into machining and they are often cost much less than a new lathe, certainly less work than making a lathe. (Heretic moment – my advice is to stay away from Myford, in my opinion they are vastly overpriced low capability lathes with some annoying design features. I'm sure I'll be drawn and quartered for that statement but even a semi clapped out well used Colchester , Harrison, Boxford or South Bend lathe is better made and higher capability for less money than a Myford, usually.) Just my $0.02.
JD