Re: 1959 10 hp tiller ?
As Chris said, many years and models use that same tiller. Just look for the kind that has two halves, split down the middle, lengthwise. OK, within that category are two different kinds of gears on the end of the twist shaft. Early ones had a stamped brass gear, later ones had a cast bronze gear. The gear type must match the gear on the motor side. They are interchangeable only if you also change the matching gear.
EDIT: BTW, the gear style change happened mid-year 1956.