Maybe they could be these... the 1280 disappearing spurs.
This page is from a '51 catalog.
From the way the description is worded, possibly they were offered as an option to owners of outfits that wished to replace their clip-on spurs with an upgrade?
We addressed this thinking once before, and I think it might be best answered by one of the Big Guns... perhaps the Good Dr. Wenk could be persuaded by David to weigh in on this?
I believe SkyDog75 and LandenLarry both have bass drums with the 1280 spurs.
Perhaps they could send us a pic of them for reference for you?
Kev