take it that this gun cannot be converted to full auto.
Were there a number of these guns produced?
Any semi-auto firearm "can" be converted to full-auto if you have the equipment and know what you're doing.
When George Numrich, owner of Numrich Arms/Gun Parts Corporation/Auto Ordnance introduced the semi-auto Thompson gun in the 1960's, he bragged that he'd spent $100,000 designing a semi-auto Thompson that could not be converted to full-auto.
Within two months, Shotgun News was full of ads selling instructions on how to convert Numrich's gun to open bolt and full-auto.
The semi-auto guns are very difficult to convert because internal parts are different sizes and the receiver is lower and a full-auto bolt can't fit even if you machined things.
Numrich Arms didn't make huge numbers of the semi-auto M1 version, the 1927-A1 that looks like a Roaring Twenties Thompson gun was and is more popular.
However, after Kahr Arms bought Auto Ordnance movies like "The Band Of Brothers" and "Saving Private Ryan" popularized the WWII M1-A1 Thompson gun and the M1 model has become more popular.
Here's Auto Ordnance's web site showing all the Thompson semi-auto guns.