The top first configuration is not uncommon. The widely held belief that the top barrel recoils more led to old days pigeon shooters using 1x3 loads in the 1st (top) barrel and something stiffer in the 2nd (bottom) supposedly lighter recoiling barrel. Many international trap guns made in the 70/80's had top first firing as well.
Insensitive clot that I am I can detect no difference between the recoil of top vs bottom and as a consequence have gotten some totally killer deals on primo examples of those horrid top first guns.
BTW the OP's gun sounds absolutely nothing like anyone's pigeon gun, Brit or otherwise. The Brits made some lovely pigeon guns and they were only never anything like that.
