If you want it in the excel, you should put in 60W into the power cell, then you read off from the graph, the frequency where it is at 12V.......(actually do it for 13.4v because of the two diode drops).
Do you need the isolation?...just thinking because i think your spec could be met by two parallel synchronous buck converters.
Also, the LLC can be changed to be synchronous of you wish......use a split coil sec and two diodes...and make them synchronous.
Also, if isolation needed, would be better to just do a synchronous full bridge converter.....give it a current doubler output so that your secondary current goes right down.