Get yourself a MT4-MT3 sleeve and you can then mount the boring head in the lathe spindle. Then you can mount larger objects to the carriage with an angle plate and have a much larger working envelope. You can also mount the boring head in your tailstock to bore round objects held in the lathe chuck.

how do you tram that thing?

At first I suspected that you were intentionally trying to convince viewers that these small machines have such limited vertical milling space that they are nearly useless. First setting a Kurt vice on, which is a wonderful vice for larger machines, but unnecessarily tall for your ShopTask 1720, then measuring the remaining limited vertical space. Next you added the additional height of a Kurt rotary base, further limiting working vertical space. Seemed crazy for determining maximum vertical space limit. Why aren't you using T-bolts locked into your table slots pulling clamps down between the table at one end and your workpiece at the other end. Presumably you use T-bolts to secure your Kurt vise to that table. That provides much more vertical working space. For workpiece dimensions which can tolerate adding your convenient vise to the stack, the measurements you described are relevant limits. My personal library includes three books just about workpiece holding strategies. Interlibrary loans should enable access to such material without buying expensive books. Very few installed Kurt vises have those rotary bases in use under them. Each additional mechanical link degrades rigidity and available workspace. Lots of those rotary bases purchased new sit on shelves mostly because experienced mill operators don't want them included and degrading in the mechanical force loop.