Three Toa tall is definitely possible, albeit with some joint issues that should be able to be resolved at some point in the future:
Note that the joint issues aren’t necessarily with the strength of the joints, but rather with the tolerances of Lego turntables allowing the joint to bypass the strength of the parts.
I can’t speak for the original post, but here’s my math which comes out to a similar figure:
The Rahi Beasts book states that Tahtorak are around 40 feet tall. Toa are around 7.2 feet tall on average. Assuming we want this to scale with the Toa Metru, a Metru build is somewhere in the mid-twenties tall in studs. Scaling that, taking a Metru build to be 25 studs tall, the Tahtorak model would be approximately 140 studs tall, or approximately 112 cm.