Resurfacing the engine block to remove nicks and low points using budget method?

I am replacing the head gasket because it was blown, mixing coolant into the oil, need to resurface the engine block as it has some deeper grooves near where the coolant was leaking into the oil from the coolant passages. I have heard that using a piece of particle board cut into the right size to get even coverage to cover the surface of the block and using some glued sandpaper to the wood and just going back and forth with as even strokes as possible will work, if done in 2 minute increments and then rinsing the sandpaper surface of the aluminum shavings to help it from not allowing the shavings to add to the resurfacing will work, although will take quite a bit of elbow grease but can be done because I cannot afford to have the block resurfaced by machine shop. I had also heard of using a thick enough piece of glass instead of wood to keep the surface as straight as possible. Any other points or ideas? I may just take the block out and then use the sanding method by flipping the engine block over and using the weight to sand it back and forth. Is the wood method feasible or should I stick to a thick glass?