I am looking for technical info? Is the pinion nut on a 1977 300d right hand or left hand thread and how hard is it to get off?

That would be RH thread! Not only tight but peened on! Most of those are also a "slotted" type of nut that requires a special socket!

UNLESS you have done differential set-up work, I wouldn't recommend that you start with that job!

You need to check PRE-LOAD on the pinion assembly before starting & that means a dial style inch-lb torque wrench.

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