The trick to level 770 is in getting the metal blocks aligned at least three times.
In this example, The top line blaster is used first, before making any moves, as that took care of 6 metal boxes immediately.
Then the blocks were lowered trying to keep metal blocks in another line for when the built up booster was ready.
The paint cans can be handy to line up the boxes, but can also be saved for some large groups at the end to clear remaining blocks and bring everything down into the bottom row for one final blast.