The Baby Pathfinder will fly very well on lines from 52 to 55 feet, when powered with an engine such as the .061's currently in use.
Try to have the finished weight in the range of 12 to 14 oz's.
It was designed for a 1/2A engine, and though slightly larger engines can be used, I would discourage the practise. One of the reasons it flies so well, is the wing loading, combined with the right power.
You'll enjoy it, it is designed to build flat on a board. See if you can find one of those cieling tiles, about 2' X 4". Pins will stick into it, and help out.