Cornelia,
I am planning this way now, please let me know if this works: Create a new Cube3 and connect Cube1 & Cube2 to Cube3 using transformations. In transformation from Cube1 to Cube3, Fiscal Year/Period will be mapped to Calendar Year with a routine to convert Fiscper to CalMonth.
Another question is, if mutually different Key figs are mapped to Cube3(KF's are different in Cube1 and Cube2), will the records be OK based on same Common Chareceteristics 0PROFIT CENTER & Calmonth?