Epoxy is used to self level on many builds to get flat surface to mount rails. You need to complete design and get some comments there are knowledgeable and experienced people on here that will advise of any known pitfalls with your design. The fixed gantry was an excellent design but he was obviously a skilled welder with a well equipped shop, I noted when he ground the gantry and thought it would be possible to some degree of accuracy with a large grinding wheel and mounting gantry on a pair rails and carts temporarily fixed & levelled to allow feeding in a similar manner. With my build and my limited equipment it was a case of the best I could do with the resources I had available so I converted a micro mill first.