If we're using the original definition of left and right, they'd technically be on the right.

The original meaning was whether or not you supported the monarchy. I'd say that a dictatorship is close enough that it applies.

Of course, politics isn't one dimensional. Even the "political compass" isn't really enough, here, there's probably an axis of the political graph for each major axiom of governance.

Honestly the best descriptor for tankies is just "authoritarian communists." That tells you where they stand better than any attempt at a spectrum or graph.