[JWL]

No, shim at the rear. Since presumably the crank thrust face is worn the shaft, if bearing is shimmed at the front, would assume a new, uncoordinated, center to center running position, farther forward than when shimmed at the rear. Too, when shimmed at the front and the clutch is released the shaft would be sent forward to the full extent of the thrust face wear. There is a limit to how much misalignment the assembly can withstand without self destructing. The limit is likely more than the described assembly might have depending on rod to rod side clearances and small end to pin boss clearance. However, it would not be wise, nor necessary, to test the limits.