The issue that I have with adding weight and therefore inertia to the non driven end of any crankshaft is increasing the possibilty of a spiral fracture.

I have seen a few of these in front induction diesel conversions and they radiate from rear corner of the intake cut away in the crank and progress towards the crank web twisting around in a 45 º spiral.

Personally, I think that the weight is being added to the wrong end of the shaft - but if the shaft is strong enough ................