It can be from 180 h.p. (Base Engine) to 375 h.p. (Corvette) depending on which 1991 5.7 liter engine you are talking about. You did not specify which 350, so you get no definitive answer.
350 hp
1991 e 350 diesel 7.3 has 190 hp
a 350 will produce around 250 hp, and a 305 about 200 hp
350 hp350 hp
if it has the 350 CI engine it has 250 HP @ 4400 RPM if its the 305 CI engine it has 235 HP @ 4200 RPM
175 hp
160 hp
it came with a newly designed 350 lt1 300 hp cam driven water pump with a opti-spark ignition
350 hp 400 tq hp means nothing it is just what the engine is rated at. torque is the actual measure of power
Is the engine the stock engine that it came with from the factory? If so, it's the TPI 350 in that case, and it has 245 HP. Peak torque would be around 330 lb/ft.
250 ci 105 HP, 305 ci 140 HP, 350 ci 145 HP, 350 ci 165 HP, 400 ci 175 HP.
factory HP in pre-1988 - - around 280-300 HP depending on carb. Nascars 350's - - over 850 HP.... if you've got the cash.