IMHO: Again mid 1950s to early 1960s is as close as I can get.

Great patches there !

I like the numbered officer insignia.

Great Bullion USAF insignia----I like these a lot

USN / USS Platte AO-24, “Primi Saesse Auxilio”. Commissioned 1939, decommissioned 1970-1971. Japanese-made Prince Rocky. Any ideas about a more precise date?

USN / TF 76 Seventh Fleet Amphibians (Task Force 76, Amphibious Force U.S. SEVENTH Fleet). Presented by Comphibforseventhflt. 1970s? No manufacturer (apparently Japanese-made).

I highly suspect these are misidentified Australian manufactured Reising magazine pouches rather than made specifically for Thompson magazines.

The Vice President of the Vet group (and a 2nd Missouri Cav man) was Camillus Nelson.   His ranch (The Nelson Ranch), built in 1872, is on the National Register of Historic Places.  https://noehill.com/yolo/yolo_image.asp?strImage=nelson_ranch.jpg

I fancy buying a pair of US Tanker trousers bib and brace as worn with the tanker jacket, ideal for winter use. I was looking at the DE Brabander MFG CO made pair sold by the Quartermaster Inspector BE company they do sizes from small to 4 XL, I have been told to get one size up  than your normal size, as these are worn over trousers back in the day. Trouble is knowing what these sizes relate to in inches. I am a 38 waist and 30 inside leg, how would you know without actually trying them on in a shop. Anyone had such a pair and satisfied with fit.  

Actually, I like the look, as is.  It looks like the handle could have been made by Auburn Button Works, which made grips for the M1 bayonet.  In my experience, even though you may do a great job of restoring this Mark 2, it will still be a knife that has be "messed with".  Since it has already been compromised, and there is no sentimental value, I would keep it as is, and the spend your money on a reasonable condition Mark2.   Just a thought. Marv