My 355 has an Eagle internally balanced rotating assembly. I recently purchased an SLP billet flywheel for it. My question is: Should I take the time to have the thing neutral balanced? What about the balancer on the front of the motor?

 

There is no "balancer" on the front of the engine - its only a harmonic damper. It is neutral balanced.

Since your engine is "internally" balanced, you need a neutral balanced flywheel. The SLP piece probably has the weight on it for the stock "external" balance.

 

Even if a manufacturer claims their flywheel to be zero balanced you should have it checked out by a machine shop to ensure it is truely zero balanced when installing onto an internally balanced engine. The last thing you want to do is take a flywheel that is used for an externally balanced engine and put it on one that has been balanced internally. Take it to a machine shop and have it neutral balanced.