I just aquired a 1979 chevy 10 silverado stepside that came with a factory desiel motor. The motor (and trans?) was swopped out for a gasoline engine, prior to me owning it. The intake manifold has oldsmobile stamped on it. The block casting has the number 554964 with a larger 3A following the number. I am looking to find out as much as I can about this motor (I know nothing about it).
Thanks  

From the info I have its a olds. 350  

I would run it as long as it runs good.                    Olds makes tough 350 engines. While I am here,Pontiacman has good knowledge. I have a 6 3/4" harmonic balancer on my 83 305 chevy motor with slipped outer ring. Will a 8" 305 balancer work with affecting my engine balance?,since it is internally balanced, Or will it affect my r.p.m s only?  

Thanks Pontiacman, I have a mystery Holley carb on it. I took the carb off and took it to shop that specializes in carbs and he said it was an old, probably factory, off of something. I know it is not the stock carb, due to the adapter plate. He didn't recognize the numbers on it and could probably find a rebuild kit for it, if it needed one. I took it home and tore it down, cleaned it all, found a lot of crud in the float shut off (which was no surprise due to the fuel overflow). I will still go down the rebuild road if I can find out if the carb is adequate for the motor. The is "stumble" off the line and I was told that it always had that even after having the carb rebuilt, more that once. I'm not sure how reliable that information is, though. I don't know if they used new parts or just cleaned it (new seal in accellarator pump would help, if the carb is big enough).
All that being said, I'm looking for the year (or approximate?) for the motor so I can look into a new factory carb for that motor.

Thanks