From my own testing, long needles are no more or less efficient than crosses. For a power generator to be efficient, all you need to ensure is that each new connected block is increasing the overall box dimension by one, and it is as efficient as possible. Therefore, weird diagonal lines are as effective as needles of the same mass, which are also equal to crosses containing the same amount of blocks.
Power tanks have no box dimension bonus, their bonus is just based around number of connected blocks. Knowing this, the best way to deal with power tanks is to simply ensure that all of your blocks are somehow connected to all your other blocks, and you will be building as efficiently as possible.
Shield blocks have no bonuses at all. The stats are simply based off the total number of shield blocks on a ship, not the number of connected blocks, box dimensions, or etc.
Hopefully this information proves useful.