The shifter problem is probably due to wear in several places. You can access the problem by removing the rubber boot on the shift lever. Then remove the snap ring etc. and the lever can then be removed.
You will now be able to look down on top of the shifting forks.
With the shift lever or a long screw driver you can now move the shift fork back into neutral.
Wear points are the groove on the "ball" of the shift lever, the square headed pin that rides
in the groove, the ball itself, the socket, the tip of the lever and the top notch of the fork.
Repairs will have to be determined by you after you have evaluated the wear points. You
may only have to work on one or two things. If the shift lever twists around it would indicate
a worn pin and groove. Over size pins were available at one time and the groove would have to be re cut to fit the oversize head or a new groove cut on the opposite side and a new pin put in the hole on the other side of the shift tower. The oversize pins also required the removal of the "soft plugs" in the side of the tower and the pin hole redrilled to the oversize shank of the oversize pin. Sometimes a big machine washer under the snap ring will help.
The tip of the shift lever can also be built up with a welder and then reshaped. The same can be done with the forks but that will require the removal and disassembly of the shift tower.