Can the harmonic balance come loose?

It was a weird situation when this thing was built too.
I did work for the shop and in return they built the motor. I even remember I saw they installed a Eagle crank, and I said to them, wth? Of course you have to use the cheapest crack out there! But they said they balanced it in the shop before the install so its internally balanced, so everything should be fine... well I guess it was 10,000 mi Fine.

It's a stoker motor too.

I'm afraid if I tear this thing apart I won't be able to stop myself either. They used some stock parts (like the connecting rods) that I'd feel more comfortable if I replaced, one head is milled more then the other, I'd like to fix that too. That's what I mean though, everything just keeps adding up $$$ But you guys know how that all goes.