I'm sure you must know this, and not sure if it's the same, but my 615 used dowel pins on the balancer/crank. Mercedes doesn't know which ones they are selling, and mine came too long. Someone had installed a set on my donor motor, and fortunately they split and ate the balancer, not the crank.

That being said I have an extra double crank pulley from my 615.912. I can measure it up tomorrow if you're curious.

I would probably poke around for a different pulley before messing with the balancer. Seems like it would effect balance. But I'm a novice advising experts.