This one is done "the proper way" :) Not I2C or SPI, but with address decoding and mapped into the main address space. Unfortunately there are not many manufacturers who still make RTC ICs with parallel bus. In fact, except Maxim there are hardly any others. Fortunately this good chip from TI is perfect for the need. Not the cheapest option on the market, but still bearable price.
Sending this one the factory way too, for prototype PCBs.