Yea glass works with cast or alloy, have done it in the bush before but ill promise you that you will be blowning gaskets after 15,000km easy or less!
Its not only about the surface being flat but the texture and cut pattern also come into it - a good example is different bore hones and grades to suits what rings your using.
Good on you for giving it ago but for the $300 it would take to hot tub it and fly cut it, its not worth all the hassle and future repairs.
Do it once properly otherwise it will cost more anyway!