Engine balancing question and crankcase pressure issue...

[FlatBlackZ28]

If an LT1 engine is balanced using a brand new weight flexplate and a stock crank pulley, would it put the engine out of balance to switch to Super Damper? They are both neutral balanced, however the Super Damper may weigh more or less than the factory unit and I'm not sure about the diameter (although I think the diameter is the same)

My balance issue is driving me crazy. I have a buddy of mine digging up the stock pulley we used when the engine was balanced.

Also, from 6k-7krpm under load, tons of oil will blow out the rear main seal. Is there a better way to vent that pressure? It's not blowing out the vent tube on the valve cover so I didn't think it would be enough pressure to blow through the brand new seal. Could an imbalance cause the oil to blow out the seal?

Thanks in advance!