Be aware that Myford change gears are 14.5 degree pressure angle (PA) whereas the more common PA is 20 degrees. This might cause difficulties meshing with other, different PA, gears. In particular you could experience rough running (with cyclic errors in the thread cut) and rapid wear but may not be a problem so long as speed is kept low. You could also use 63 teeth as a conversion gear without much loss of accuracy. Have you tried HPC Gears of Chesterfield, Derbyshire ?