Unfortunately i have nothing left out of a 2H of 12HT.
The harmonic balancer should swap over. The crank itself should also perform in a 12HT, the only thing i would be worried about is breaking the crank. That's what happenend to mine years ago. It broke in a spot with more meat then a 2H...
I've had 2H and 12HT cranks side by side. They would definately swap out, but the 12HT crank has more meat in some areas.
Not all, but some off the journals have a wider casting. Not sure if my explanation makes sense. ;)