Wildo, I think you misread what I said about referencing the level. I meant getting repeatable reading of the lathe bed's level. A surface plate won't help with that. For getting the level trued that's a whole 'nother matter not for this thread.
I agree with what Janvanruth said about nuts and bolts. To get the twist or bow out of the bed you may need to push AND pull on the bed mounts to get things straight, level is just an easy reference to do that but nothing NEEDS to be level. To level the whole kit and kaboodle adjustable feet are convenient on the mounting frame or table. Just compensating for an uneven floor really requires adjustability. But I would never rely on gravity and machine weight alone to straighten the bed out. In fact, to eliminate the torquing of tables and benches, or reference plates, only three points of contact are recommended so only the machine and it's mounting surface are acting on each other, reducing if not eliminating the affect of other forces.
So, two things are being discussed here, as usual when this topic comes up, "level" and "straight". Even the title of the thread conjoins the two ideas, which clouds the discussion somewhat. They are not the same and not mutually exclusive. In addition, when talking about "leveling feet" I'm not sure where you are applying them, between machine and bench or bench and floor. For my purposes, and I think for most, rigidity and straightness of the bed are paramount. To achieve that things need to be bolted securely from moving up, as well as down and sideways. I'm not so sure leveling feet achieve that end. I've read several discussions on the topic and one common consensus is NEVER use
cushioned feet on machine tools. Seems that put nuts and bolts well in the running for your application. I can buy a LOT of nuts and bolts for $83. Further, you have a lathe capable of turning all sorts of couplings, feet, points, whatever to achieve a secured machine.
Mine is but one opinion on a topic that I believe concurs with the majority but you can always find contrary opinions on any topic should it suit you. I hear they're relatively inexpensive. Maybe so, but I've found the better ones were obtained at greater expense.
Mark