my window for my extension measuring 1.2 by 1.2m is gauge for height in brickwork but not blockwork. Do i cut the blockwork for the lintel to fit in or jack the window up to the height of the nearest gauge on blockwork: 1.350m
Its quite normal to have to cut a block down to finish level with the top of the window. You may have to cut down the blocks or use brickettes to go over the top of the lintel as well (depending on design of lintel), leveling up with the main blocks either side in the process.
Don't move your window up as it will probably be lined up with others or a door frame elsewhere on the building. It is common to make the top of the windows the same height as the top of the exterior door frames.