In 1915, A. Einstein described gravity in the theory of General Relativity on the basis of differential geometry as a curvature of a 4-dimensional space-time. From 1920 on to the time of his death in 1957, he tried to unify electromagnetism and gravity in a description resembling the one used in General Relativiy, but with no success. In doing so, he favourably noticed the 5-dimensional unification theory by Th. Kaluza. From 1949 on B. Heim worked on a 6-dimensional unification theory of electromagnetism, gravity and quantum mechanics. Sometimes B. Heim’s Unified Structural Quantum Field Theory USQFT is even claimed to be the long sought Theory of Everything. Durings the 1980’s B. Heim published versions of so-called mass formulas based on USQFT to calculate the masses of diverse elementary particles. Indeed, these results were in agreemet with the experimental mass values as was proven by H.D. Schulz from DESY. Therefore, USQFT is worth to be reconsidered by now.