I think removing the cover of the transmission is a good barometer of the overall condition of the transmission. The following pictures will point out wear areas that are going to effect your overall transmission performance.
If you want to remove your cover you should follow the steps in your manual as well as thinking out what you are getting into. First drain your transmission fluid, next plan on how you will reseal the cover so have a gasket on hand or the sealer of your choice. Realize that it will not be easy to see into the transmission because of your head room in relationship to the floor of the car. For me it is easiest to use my camera for inspecting the inside condition of gears etc. As you remove the linkage inspect it for wear. An out of round ovally worn part should be repaired (weld a new washer over the the damaged area).
A lot of what you will be looking for is worn/damaged parts. When removing the cover you do not remove all of the bolts. In one of my above posts it shows the cover with two bolts still in place. They are used to attach the guide bar to the cover.
Remove these two bolts only with the cover on your workbench.Also it is easiest to remove the cover in neutral. When taking the cover off do it slowly so you can see the position of the clutch and the gear that rides on it. Below I included a diagram of the transmission so you can become familiar with the names of the parts. The cover parts will have to lineup with the clutch and gear to reinstall the cover correctly. And yes it is possible to not lineup the yokes with the clutch and gear. I have been there and done that. In the best case scenario it is always easier to work on the transmission off of the car so you more easily see how things are lining up.
Several of the following pictures show badly worn parts. Notice the interlock that the linkage is attached to and the one 2nd gear/high speed yoke. If you are looking at this degree of wear you can imagine why gears are grinding as you shift, or why a gear can slip out of position.
Diagram from Chevs of the 40's also available on line in our online parts catalog
http://chevy.oldcarmanualproject.com/parts/1929_54/index.htmThis linkage is attached to the interlock. It is probably not unavailable as a NOS so repair it as I mentioned above.
The above picture and the two pictures below show a worn interlock. Another challenge to find a replacement part. Maybe another candidate for a welding repair.
The yokes in their neutral positions attached to the guide bar.
Underneath the yokes you will find a spring and 2 ball bearings.
Be careful removing the yokes so you do not loose the bearings. If the yokes do not slide off with brute strength then use a brass hammer to gently remove one. Once the bearing is exposed the yokes will move easily off the guide bar.
Reinstalling the spring and the bearings requires you too have the bottom yoke in the neutral position. That position has the bearing in the middle hole of the bottom yoke. The spring will then stick up less than a 1/4 of an inch. If it sticks up more then it will be very hard to depress with the bearing on top of it. This also means that the bottom yoke is really not in the neutral position. Carefully put a 1 inch wide putty knife on top of the exposed bearing and gently push it down inside the guide bar. Next slowly scoot the yoke over on top of the bearing as you move the putty knife away from the yoke. Please be aware what might happen if you are not careful,
the bearing could shoot away from the guide bar/yoke and now you have to figure out where it flew to!!! Do not try to pull the shaft through the seal on the cover without removing all the burs off of it. Rarely do you find a shaft where someone has not taken a pipe wrench/etc and tried to shift the transmission with it. Pulling a chewed up shaft through your seal is going to damage it and cause transmission fluid to leak. Be cautious when removing the interlock to clean up its shaft before trying to get it out of the cover.
It is very important that the bolt is tight on the interlock shaft. If it is not then you can imagine the amount of play that could be in this piece. A part designed to move a 1/4 of an inch could require 3/8 of and inch or more to move a yoke.
I am sorry if this needs some editing but I only have so much unsupervised time.
Please comment so we all can better understand this component of our transmissions.
Thanks, Mike