here are some quotes from an SAE tech paper "Subaru New Horizontally Opposed 4-valve Engine". The paper was published in 1989
The first few quotes relate to all EJ series engines made, and the last couple of quotes pertain to only the turbo motor and obviously not to the STI with the higher rev limit.
"The connecting rod and cap are made of forged steel..."
"The crankshaft is made of forged high carbon steel with five main bearings and eight counterweights."
"For the 2.0 Lt DOHC turbo version, medium pressure diecast aluminium crankcase is utilized to secure the higher rigidity necessary with a closed deck"
"A double mass harmonic balancer is adopted to disperse the torsinal and bending vibration up to the 7500 rpm maximum operating speed."