Hi, I would call Moss and ask if the listing is correct.
Here is my experience with the wheels on my modified TR-3a. I bought (4) used Moss wheels off of Ebay. They had Moss stickers with part numbers on them. They have "Made in UK, KN and S.C.P." cast on them. 15 x 5.5"
I have the 4A upper control arms with the Moss Europe adjustable upper control mount and the 3 deg trunnions. The spindle is stock TR-3a. I have a stock TR-6 sway bar. The wheels hit the control arms and sway bar so I did a little grinding on the arms. I dont know if a stock 3a upper control arm would hit. I added a 1/4" spacer between the hub and the wheels and added longer wheel studs. I got them from Wishbone Classics. The Moss Lug available at that time did not work well, They only engaged about 2 turns. I went with a lug that had the same conical end and a extension for more threads. I got them from Keystone mags.
Looks like Moss lists a 1/4" spacer and longer lugs in the TR-3 catalogue.
After all that, I would do it again in the minute. Straight, round wheels are worth the effort.
Good Luck
Roy