Buy new tubes with right angle centred brass stems. Redrill nothing, go together like a piece of cake, through the provided half holes. If you do go the redrilling route, fit the provided black plastic plugs in the original holes, be aware that the supplied tyres are very thin in the bead and if you upgrade the tyres later, their bead will be much thicker and once again the stem won't come out the hole. You will then have to weld up the hole and redrill further from the rim flange.