The first record I show of an AR mount is 1949. That reference says it's a Firestone design, later references call it a Kelsey Hayes design. Maybe both are right since the companies teamed up on things during the era. There's also an old style AR and a new style AR shown in a 1953 K-H catalog. Yours look old style.

http://i286.photobucket.com/albums/ll89/truckdog62563/Wheel%20Profiles/ARsideringandlockring.jpg

As far as manufacture date, on the K-H wheels I've messed with I've never found part numbers or dates like I would on Budd or Motor Wheel. The wheels don't look like MW to me, so if they are Budd the part numbers will be on the back rim lip and the manufacture month and year will be stamped between the lug holes on the face side.

I'll ditto Grigg's safety statement. Also, the old literature says that the three piece designs were developed for use on the bigger model trucks to allow the side ring to move with the tire bead under heavy load. Thus reducing chafing of the tire bead. Glad you got them and that they look to be in good shape. Stu