Substantial information on nuclear shells which determine the stability of superheavy nuclei, can be achieved from the measurement of decay properties of isotopes of element 120. Using existing data measured up to elements 116 and 118 at FLNR in Dubna, estimates of shell-correction energies and fission barriers are deduced and compared with model calculations. The results indicate that the probability for re-separation of target and projectile like nuclei in the entrance channel of the reaction is less then assumed in some of the existing cross-section calculations. This finding together with technical reasons favors the reaction 54Cr + 248Cm for synthesis of element 120. A first part of the experiment was already performed in 2011. The results will be presented in a forthcoming paper.