Did you really mean transferring the Savsys, or just your user data from the save entire system backup? Obviously the V4R4 OS on the Savsys tape will not work on a model 520. You should be able to restore your user libraries ok, but there are considerations such as software that’s no longer supported under V5R3. Client Access for Windows 95/NT and Officevision are two that quickly come to mind. Also, if you have user data in QGPL and QUSRSYS libraries, you have the issue of restoring the user data to the V5R3 versions of these two libraries. In addition, other changes such as SNA is not supported over the gigabit ethernet ports have to be reviwed. The best answer would be to review the Memo to Users documents for each version/release from V4R5 to V5R3 for items that may affect your installation.