Hi hydrogirl:
Well, question: Does your Motor Control Center has a main disconnect or a maximum of six disconnects as required by NEC?? This shall be of sufficient size as to deal with your 4160V XFMR. If the MCC comes with a main disconnect or has not more than 6 disconnects, than you will save some $$ buy not getting a fused disconnect cabinet. (Of course this is if you're only using this switching cabinet for you MCC only, otherwise you can use it for later electrical additions)
What is for sure is that you will need a way to disconnect your MCC (i.e. electrical service) and this is required by the NEC, check NEC 230.70 Part VI. In other words, there is no way you can just go with the primary side fuses.