Why must everything be a hassle when trying to buy parts? Example, spark plugs

both selections are for a 1963 Plymouth 426 wedge. (7.0 liter) so, why is the Fury assigned the GR5 and the Belvedere assigned a XR5?

https://ngksparkplugs.com/en/part-finder

So I called the help line, Paul answered (awesome guy!) and he took a sec, looked over the issue, and said he's going to get the website guys to straighten this out.

Why does it matter? The GR5 and the XR5 are 10mm different lengths, and the longer one could just smack into the pistons.