Yep, to me it sounds like the linkage should be checked out first if it's going forward in N. I don't know how you could tell if a valve body is bad by looking at it. But I bet there are hundreds of dead 560's with valve bodies that you can steal for extermination.

Also, as you indicated flaring, do you know if the vacuum modulator is good? If not, it will cause shift flairs.

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With best regards

Al