You cannot use the later converter(68 up) with the 63 trans. The input splines are different. It changed between 67 and 68, the same time as the crank "pocket".
PS: It is possible to use the late engine (68 up) and late converter with the early (67 down) trans, by installing the late front section of the trans (pump, input shaft, clutch drums) into the early trans.
PPS: You cannot install the later "Low gear" planatary gear set into the early trans, as the internal splines on the output shaft are different then the splines on on the gear set.