I need a 36 .inx60 .in base with offset dran. Can I cut off 12 .in of the 36 .inx72 .in shower base?

Yes. On a center drain you would cut down from both sides but on offset drain you can make a cut just on one side to maintain the offset drain in the same position. Make sure you maintain the lip on the edge, the wedi video will show you how to cut on the shower base.