welcome.
The "post" you speak of

Is it spring loaded? To me it looks like the old shifter is out of an older bug which are slanted back and the post is to kep it from rotating. The 74 should be staight up and down and able to rotate.
Can you post a pic of the whole shifter- the one you took out?
From my experiences those aftermarket shifters leave a lot to be desired. Was your old one giving you problems or just want something different?
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derf
No matter where you go,there you are.
My post are my opinion of what has worked for me but are not the gospel

What I post is what I do on my cars. I am here to try and help not to impress or boast