The valve body can be changed but you should consult with someone more knowledgeable than me to find out which ones can be used in your particular transmission.
Usually, unless the transmission has sat with water in it or run without a filter, the valve body isn't the problem.... What's the symptoms?
Is that what you think the old problem is newbuds?
You can replace the valve body but in your case I think it needs to be from the same year (66 or it this a diff tranny). There were a few changes with the valve bodies and ones from some years won't be proper for other years. Valve bodies don't really go bad, just the components inside wear out. A shift kit will give you the springs and little balls and gaskets to rebuild a valve body. Consult the fourm before going ahead with this.