The steering coupler size maybe one of the few things I don’t know much about on these cars.
I do have a few rebuild kits in my garage (for my own projects) but other than that, not done one yet.
I went out to look at the one on my Volare, and it is also 3 inches long.
Looking at it, I noticed the retainer had popped loose and is leaking grease out. Sigh, something else to fix.
The part number for ’83 is 3837669 (or at least I think this is the part you are looking for, #24 in the picture).
I then went to look up the ’71 Imperial part # and came back with 2996857 (for all ’70-71 cars with P/S).
No mention of year truck so I looked it up in my ’78-81 Truck manual and came up with 3579522 (B Vans with P/S) and 4115549 (pickups).
Other than that, I can’t comment any further.
BudW