I used one of those once, and yes, it is a "Ford part number". I probably will stick with the 51515 without the R because IIRC the R has a more porous filter material. If I'm wrong, corrections are welcome. I also have TTi headers 1⅞" 70 Roadrunner 440 6bbl.
I have never heard of that, is it widely available or mostly online for those who live in CONUS?
