Well...if you removed the overdrive by taking out the 4 big bolts that hold it to the back of the gearbox casting.... that will most certainly cause the mainshaft to slip back a bit, which in turn will most certainly mis-align them shift dogs...in the picture, item #36 of which there are 3, held in by springs item #37.

Now...taking it apart.... There is a good discussion on the topic in the archives started by me sometime back in November. A couple threads actually. I couldn't find it, but its well worth your search of the archives. Also, read and print the vclassics article and take it with you to the garage. It will help.

http://vclassics.com/archive/tranreb.htm

Short story though... I'd say there is a very slim chance that you can pull the main shaft back far enough to re-align the dogs and get the springs back in place, but I sort of doubt it. I reckon you will have to pull the rear shaft. To do that, you MUST drop the layshaft and all its 36 little roller bearings. Getting that all back together is the tricky part... but hey, I did it twice during the first day I ever tried it, so it can't be that bad...

When you are first in there, you might think you can pull the main shaft without dropping the layshaft. and...you can, but you'll do some damage, and you'll never get it back together that way.

Good luck!
-Matt