Spark Plug Discrepancy

I have a 1992 Buick Century with a 3.3L V6. The spark plug specified in my owner’s manual is AC Delco R45LTS-6. When I researched this part number on the Autozone Store website, I received the warning “This part DOES NOT FIT your vehicle”.
Instead, Autozone recommends AC Delco 41-601. I compared the specifications for both plugs and found two minor differences. The original plug has a ribbed insulator and a 2-12-220 resistor (don’t know what this number means).
The plug that Autzone recommends has a smooth insulator and a 2.5-12-220 resistor. Can anyone explain this discrepancy? Were there changes in environmental laws that changed the correct plug type?

The AC Delco site agrees with the Autozone site. I guess the R45LTS-6 is obsolete.

I believe that the part’s numbering format was changed. The earlier number was quite descriptive compared to the newer part’s numbers. As I recall the R meant resister, the 45 was the heat range, L had extended tip, TS was tapered seat and the 6 meant pre gapped to .060.

But my memory, like my good looks, isn’t what it used to be.

I forgot to ask another question. Should I replace the plugs when the engine is cold or a little warm?

I believe it’s preferable to let the engine cool down enough that you can touch it.

Cold…especially with an Aluminum head.

Straight from the horse’s mouth

I also agree with the others . . . go with the 41-601 says this is the conventional plug for you