what happens if your 904 shift linkage isn't adjusted right?

Well if the fluid is clear and it ain't broken, don't fix it. Good catch! When I was in high school I rebuilt 12 torqueflite transmissions and every single one of them failed due to the first/reverse servo piston seal failing. It seems like 50 years later there have been so many rebuilds and modifications done to all this old stuff that you don't know what your dealing with. As an example I have done a couple shift mods to fords where they give you a template and you drill a small hole in the valve body orfice plate...who will ever know that in the future?? Good luck!