Actually "1st Lt" is the correct abbreviation. It is the Army that uses "1LT."
That doesn't mean the documents are genuine. The correct abbreviation for lieutenant colonel is "Lt Col" (no periods), not "Lt. Colonel." And the 147th Fighter Interceptor Group is "147 FIG."
The documents have serious, serious problems.
In the Air Force...the proper abbreviation IS 1st Lt now. Not sure what it was back then but the latest guidance is to write it as 1st Lt. This is for Air Force only. The army is still different. Also...Lt. Col. is the proper abbreviation now. Up until the change earlier this year...it was LTC...like the army still is. Not sure what the abbreviations were 30 years ago...but I suspect the person wh did the hoax looked at a current rank abbreviation guide.