Yes, I believe yours and mine are the same, and also the same as on all the late '69 Legends cars I observed at the nationals last week. The same nut type was also on the unrestored '69 Z28 (blue/white) - a May'69 car.
Attached are a few photos:
photo1) the rear-most nuts as originally installed for holding the spoiler.
photo2) the 7 original nuts from removing my spoiler for cleaning and repair (one of the longer forward-studs was broken and the nut was missing),
photo3) one of the longer studs from a fwd spoiler position with the flange and two differing thread types. What made the studs unusual was the existence of a 5/8" diameter 'flange' in the middle of it's length, with machine thread studs on one side of the flange, and a self threading type thread on the other side (for installing into the spoiler itself). Note: the rear-most studs were similar to the forward ones, although with shorter machine threads on the 'nut' side.