You could have a couple of different problems here. Last I knew, 81 cutlasses only came with one motor. The oil light flickering likely means you have low oil pressure but you must first determine if that is accurate. Most techs will use a manual pressure gauge but you could try replacing the oil pressure sender first. It it really is low, the you could have a bad oil pump, restricted pick up screen or worn main bearings.
Your next problem with lack of speed could be the result of the smoke issue. You may have a plugged up catalytic converter. You need to read the trouble codes the check engines light is informing you about. here's how you can do it.
Ground terminals A and B with the ignition "ON" and engine not running. The system will enter the diagnostic mode. In this mode, the computer will display a 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A 12 consists of one flash, a short pause, then two flashes in rapid succession.
After 12 is displayed, any stored trouble s will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All s are displayed 3 times each then a 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.
ALDL Connector (Located Underdash)
The ALDL diagnostic connector is located in the passenger compartment.