Raimey,
That looks like a typical Vienna snapper correct? If so, one of the examples I located of Seifert marked mounts are of at least a similar type, which as you say, would correspond with his time in Vienna nicely. I still don’t know how to post pictures on this forum, but here are links to some existing examples. I just located an example of a gun apparently marked to him as well sold at Hermann.

https://veryimportantlot.com/en/lot/view/hahnbockbuchsflinte-seifert-bratislava-346489



Here’s a scope that I’m thinking has some Czech influence in the mounting?

https://aukro.cz/druha-svetova-valk...zielvier-j-seifert-bratislava-7101140586




Here’s the Vienna-ish style? The front retaining mechanism seems a bit different than I’m used to?

https://www.lugerforums.com/threads...utm_source=google&utm_medium=organic

Mine is different from all of these yet again on a double rifle.