Champion offers a #518 spark plug which is the current version of the W18. These have the correct 8-32 threaded stud at the terminal end of the plug. However, these have about a 3/4" reach. "Reach" is the distance from the shoulder of the plug (where the gasket seals) to the end of the threads. This is not a problem for piston clearance, but some members feel that "reach", along with heat range, are important factors in achieving a smooth idle.
Older Champion plugs, like C16C, and the old original C4 plugs had a 5/8" reach. You can sometimes still find these at swap meets or on the internet. These older Champion plugs also have the 8/32 threaded stud for the terminal.
I am not sure what the reach is on the W16Y plugs that you found is. But these sound like a slightly colder version of the 518 (W18) Have you tried them yet?
There are also other plugs available in Champion’s "W" series, like W14, and W10. These are progressively colder plugs, but I have not tried them.
Autolite also makes a current compatible plug, #3076. This is also a 5/8" reach, like the old original C4 plugs. I have not used them personally, but I know that other members say anecdotally that their cars run better on the Autolite plugs. These are also available on the internet, like at http://www.autolitesparkplugs.com, at a good price, too!
I hope this answers your question on spark plugs.