one can use a spare chuck and turn it with your hand, going up a couple drill sizes at a time, or use a cordless drill at a somewhat slow speed, [also a couple sizes at a time.]
lightly clamp the valve body in a vice, using two pieces of unmolested plywood [without dirt, metal chips, etc embedded in them] covered with two pieces of clean cardboard, will hold it at an angle that is comfortable for you to drill.
just be sure you don't use anything in the clamping process that will mark up the valve body.