Try removing the low-reverse linkage rod from the shift arm on the column, then shift the transmission into neutral. Be sure to block the wheels so that the car does not try to roll off. Try to move the shifter into neutral as well. If that works re-attach the shift rod to the column and see if the transmission will shift normally. If the transmission will shift normally, that should fix the problem. If the shifter is still locked, remove the 3 speed gear shift lever from the column and inspect the end where it goes into the column for damage. These would sometimes break a chunk off the end of the shifter.
Dave
