The crowned R indicates rifled barrels > 8mm after 1897
Yes, it does carry the post-1898 Smokeless Proof mark, which could be requested by the maker at an additional cost. It is however the later stylized lion but I can't find when it was first used. It is typically used on post-1910 shotguns.
It does not have a lettre annale so proved prior to 1922
The Belgian proof house did not have a reproof mark; there would be a 2nd set of marks
The '557' and 'EXPRESS' have different fonts but I haven't seen enough Belgian BPE rifles to know if that is abnormal
