Alas...I have but 4 aluminum butts, LOL. But one does sport a DST. I've never stumbled upon one of the lock-less "F" actions.
Frank will know more, but I think the DST's were all adaptations of firearm triggers. I know back when my pal Gaines Blackwell was collecting, he discovered that the Walther and HW ones differed, and that the DST in the Walther LG 53 was not the same as in the LG 55.
Today I've been studying and enjoying this thread all over again, LOL...! What a marvelous group of collectible air rifles.
Frank, I'd really love to see more close-up photos of the two DST guns! No. 8275 has some very interesting details, and the gun combining early finger-groove Tyrolean stock - AND "F" action - AND double-set triggers, may be the most unique HW 55 in captivity!