chevy 350 no oil pressure

i bought a 1993 suburban 2500 4x4 automatic it had 175000 miles on it and a 350 engine. it was smoking when i bought it not from the engine compartment black smoke. not to bad but like what it would if you sprayed wd40 on the manifolds. i drove it 30 miles and the oil pressure was at about 50 at first then it dropped gradually. i passed a car and floored it and there was so much smoke that i could barelly see the cars headlights. i drove it further and the oil pressure dropped to zero and quit running. is it blown and what do i need to do to fix it?