The nickel Pre-18's, 18's, 18-1's and early 18-2's we've handled over the years all had blue front sight bases and blades (with or without red inserts) which was standard prior to the mid-late 1960's. The ONLY question: Is the finish original ? As in, 'N' stamps on; left grip frame, cylinder face under extractor star and bottom-flat of the barrel. If not, the nickel-plating isn't original.

If it IS real, a mid-range number between 3 and 6 followed by three zero's isn't outa' line.

DC