Don't convert that. Look for a road bike with 27 inch or 700c tires and a two piece crank. You want an old racing style bike, with drop bars, those bikes will convert the easiest. Also you need the smaller bottom bracket size, start looking at bikes as you pass em outside, you'll notice crappy bikes have a huge bottom bracket, nicer ones will have a smaller 1- 1/2' diameter one. Not a Peugot, or any 3 speed. Search Craig's list for "ten speed" or "road bike."

This bike here would make a nice grocery truck, just give it a big Wald basket.