gallatin:
Further to my last:
Just found this pic which explains why the Greener 'Empire' has been a popular candidate for a DR conversion here in Australia.

Both these shotguns are 2 3/4 chambers, proved in the UK for 1 1/4 oz loads. Greener 'Empire' on the left, Hellis game-gun on the right. Note the length of the bar, and the relative lump dimensions, particularly the front lump.

You should be looking for a duck-gun or pigeon-gun which approximates the action on the left, rather than the one on the right.