balancer, flexplate, and converter alignment

The balancer is keyed & the flexplate only bolts up one way to the engine. The only thing that could go wrong is to use a balancer that didn't match the engine balance, like a 28 oz balancer used on a 50 oz balance engine.

jrichker is correct. At first glance, the flexplate appears that you could bolt it on incorrectly, but the mounting holes aren't evenly spaced, so you'd have to spin it around until the holes line up correctly.

On the balancer, the formal procedure is to take the new one and the old one to the same balance shop (if possible) and have the new one checked or balanced to match the old one.

In practical terms, you could bolt it on, and probably be no worse off than stock.

However, for reasons I don't fully understand, I had 3 balancers fail on my 79. The original slipped the outer ring and shook like heck. The next two just cracked, one breaking the bolt and fallingl off. Both were oem Ford dealer replacements.

I put the original 78 t-bird stock unit that came with the crank on it, and its run fine, to 6k, for about 6 years now.

The replacement for that engine got balanced and a Fluidamper, that has been fine since 00.