I can't answer whether this is an externally or internally balanced engine, but I want to ensure that you know how to put the new balancer on properly.
First of all, I hope the crank snout is okay. There are two steel dowel pins that key the balancer with the crankshaft. If the front of the crankshaft is chewed up and the half cylinders for these pins are screwed up, you will be screwed as well.
IF the crankshaft is okay, do not simply place the balancer on the end of the crank and tighten in place with the bolt. This is very possibly what caused your failure to begin with.
To install it properly, you will need a harmonic balancer puller. Place the balancer and pins in place, with the balancer slightly counter clockwise of where it needs to be to align the pin holes. As you draw it down with the bolt, it will turn slightly. Draw it down a few turns of the bolt, then remove the bolt to see if it is aligning properly. If the balancer reaches the pins and is not perfectly aligned, pull it and try again. Under no circumstances should you continue to tighten the bolt if these pins don't perfectly align. You can and probably will destroy the front of the crankshaft.
Best of luck,