That 14.75mm drill bit is equivalent to a 37/64 standard bit. But as you might recall from a previous post of mine- if you're using a hand drill, I recommend that you use a bit about 1/64" smaller than the recommended size... which would be 9/16" in this case. That's a common enough size, and I'm sure you could find one necked down to 1/2" at just about any tool store.
You can drill a hole that size in an engine block with a hand drill- I've done it before. But you've got to be careful, go as slow as you can (it'll require very little downward pressure since the hole is already 12mm in diameter). It'll make a mess, but you'd might as well just fill the bolt hole with oil (if it's a bottoming hole). Also, get some masking tape, paper, rags, whatever you have handy- and cover up everything else on that deck. The last think you want is to get metal shavings in an oil passage or in a cylinder.
Tom makes a good point about the tap handle. In sticky situations in the past, I have got by turning taps with small 12-point sockets, adjustable wrenches... even vice grips. If you're comfortable using a tap and can get it straight (don't start making threads until you KNOW it's straight), then you can get by this way. But if you're not sure, then that might be the next tool you have to hunt for.
Also, for what it's worth, the required drill for a 12mm X 1.75 helicoil is 31/64- which will fit in a 1/2" drill.