The Austrians make.. interesting... guns.
I am saddragon that my jury-rigged magazine floorplate idea gets no mockery nor conjecture on if it'll work. :V
Well we wont know if it's dumb or not until you test it out
I'm guessing you have a Mossberg based on the description (ok, so it's a total guess). Having no idea whatsoever as to what sort of fabricating skills you have, I can't really speak to if your fix will work. Given how simple the factory mags are, and that you're a clever dragon, you should be able to make it work at least "ok".
The only place I can forsee a ton of trouble is in re-sizing the spring. The pressure required to reliably feed anything relying on blowback is a bit of a fixed commodity. Too little pressure and it won't feed. Too much pressure and it will cause the action to bind. Err on the side of "way too much", as it's only a 25 round spring.
Worse come to worse, I could probably walk you through how to make a working 5 round mag out of it.