I believe that we had a 24" auger that would run on a 743, very seldom used as most holes were for fence posts.
A T300 shouldn't have any problem swinging it, depending on soil conditions, but that's a factor for everything. Depth will probably require an extension, I guess the only way to know is to run up the auger head to full height and measure.
Here's a chart from Bobcat with some numbers.
Getting a perfectly clean hole might be difficult without flutes all the way up to clear the spoils, and it's a bit too deep to hand clean.
Thinking about going into the vertical cemetery business?