"what l am really after is a sort of list with brands of shotguns"

I have used a lot of German guns for conversion, many do not have a name on them, other than where they were made (i.e. Suhl). As Daryl S. mentioned the BRNO actions are very strong and would warrant even a more "updated" load than what he mentioned. That does not mean that you can try and load them to .458 Win. Mag. pressures! But you can move up to the 30K-35K PSI range. Other German actions that I have used (for .450-3 1/4" NE, 450 #2 NE, & .470 NE's) are Simson, Simpson, and Merkel - most in 12 bore, but my first .450 was 16 bore Simson, and it is still shooting fine (though it is just a touch light for the cartridge). I have used two Huskvarna action for 45-70, one was a model 51 hammer gun with back action side locks in 12 bore, and the other was a model 52, 16 bore with front action side locks. This is by no means an exhaustive list, there are a lot of suitable donors out there.

If you want to stick to the lower pressure "trapdoor" loads, there is a almost a limitless number of suitable donors.

Hope this helps.

Ellis