Whether one is unsafe to shoot or not is really a crapshoot.
There was a HUGE range of quality coming out of Spain in these S&W copies, and it's really impossible to tell the quality.
Some of them used wrought iron frames AND cylinders, and are barely adequate for use with black powder. Smokeless powder, a +P .38 Special, or god forbid a full bore .357 Mag (yes, you can fit a .357 into SOME of these guns) and you can have a really interesting time on your hands.
Generally the better quality ones will show up in their level of fit & finish and the marking of a specific caliber on them, but that is NO SURE WAY TO TELL.
Information on most Spanish guns of this period is scanty to virtually non existent.
Over time, most people who have a depth of knowledge and exposure to these guns generally have adopted the position that they were, in most cases, cheap as hell to begin with, weren't blessed with an overabundance of quality ingredients or oversight in manufacture so, like the cheapest brand of generic hot dogs on the shelf, are really best looked at and not used for their intended purpose.