Mike,
A bit of prodding maybe? SoTwin, take the forend off. Operate the mechanism and you will notice a "block" for want of a better word, that engages the hook on the underside of the barrels. There is a set screw that you will see on the block. Loosen this and give the pushrod a half turn clockwise. Try the fit. Repeat as necessary. Go very slowly or you may not get the forend off!This is bad, half a turn at a time!

Chief