I think that might be a Laurona, a Spanish shotgun. They were an inexpensive gun, an entry level SXS. If 70mm is stamped on the barrel flats it should be fine to use with modern 2 3/4" shells.
I'm not clear on "if they were a Greener crossbolt?
What do you mean by that, I'm curious.
A pic or two would help.
Mike