There was never a production "Tanker" M1 Garand rifle. The standard barrel length is 24 inches.
The gas is feed to the operating rod only a couple of inches from the end of the barrel. Any attempt to shorten the barrel will effect the operation of the gun. While it might be possible for a knowledgeable gunsmith to shorten the barrel and the gas system including the operating rod, it is doubtful the 'Tanker" gun you are looking at was done right.
The bottom line is don't buy a "Tanker" version. It is a kludge made for appearances only and the chances of it operating reliability are less than 50-50 in my opinion. $900 will buy you a very nice M1 Garand that is not molested which will keep its value better than a "Tanker" version.
CMP sells some very nice M1's in various conditions and someone who has jumped through all the hoops to get one might be willing to sell it for less than $900.
Take a look here:
I got a completely rebuilt M1 Garand with a new near match grade barrel (the "Special" grade) for less than $1000. The Service grade at $625 is an excellent rifle (I bought two of those, both excellent). Now, you have to qualify for these CMP rifles (and you may??) but there has to be one of these out there someone bought and is selling for the same or near the same money.
Do yourself a big favor and don't buy a "Tanker". You may be sorry if you do.
Also don't fall for a "Matched" number gun. There was no such thing. The numbers on the parts are the part drawing numbers. A "correct " gun will have all parts from the same time period. These guns were re-built many times and parts got all mixed up in the process. Unless someone has searched out all the "correct parts", you'll not find a "correct" parts gun today. Even CMP is sold out of the "Correct" guns.
An M1 Garand is worth owning. They shoot well and are a big part of our US Military history. Ammo is good old 30-06 and Greek surplus military contract correct ammo is available through CMP at 192 rounds for about $100.