How much horsepower is there in a stock 1990 305?

The LO3 305ci v8 used in the 1990 Silverado, Camaro, etc. was rated at 170hp @4000rpms/255ft-lbs @2400rpms.

The LB9 305ci. v8 optional in the Iroc Z Camaro was rated:

automatic - 210hp@4400rpms/285ft-lbs@3200rpms

manual - 230hp@4400rpms/ 300 ft-lbs@3200rpms