Nate-Dogg,
Per your request, I'll try and help you get some answers. I am an authorized Randall knife appraiser but those appraisals involve methods and restrictions similar to Joe's authentications, i.e.: Sending your knife and sheath (if applicable) to me for proper documentation. Naturally charges are incurred, both shipping & insurance "both" ways plus a $50.00 (minimum) fee. A photo and appraisal will be returned with your knife.
Having stated that, I can tell you that most chrome-plated Bowies I have dealt with were 1950-1960's range but a few orders were still taken into early 1970's. The sheath could be Heiser (So stamped) but many were Johnson roughbacks, more specifically, Maurice Johnson, tight-stitched roughbacks. A wide stitched Bowie sheath would be too "new". The snaps could be brown button or baby dot.
As to value, that would be researched and part of the appraisal, especially for insurance purposes. I will tell you that the last one I sold went for $1600.00, complete with a JRB sheath with 2-textured sided grey stone.
Hope this helps, Capt. Chris