This will come across as dismissive but ALL factory steering boxes have some degree of on center slop.
I had a Firm Feel Stage 3 steering chuck in my '70 Charger and got tired of it. I had slop like this:
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Looking at a dial clock, this was like between 10:30 and 1:30. Once the steering got past the slop, the effort was high and good. It was totally annoying for any type of switchback roads because I'd be at hard left then to turn right I'd have that slop to get through before the car would respond.
My steering chuck had less than 15,000 miles on it. The coupler was fine, it was the internal guts of the steering box that were worn. This happens with all of them but is more noticeable when the steering effort is higher. Simply put, a stock steering box steers so easily, you barely feel the on center slop because once the tires do start steering, the overboosted system takes so little effort to operate.
By the way...you likely didn't have a "rag joint" since they first showed up in the 1973 B body cars. No A body ever had a rag joint in the steering system.