mike, do u know for sure thats an olds 350 and not a chevy or pontiac 350?
the olds 350 had an oil fill tube in the front center of the motor that extended up about 12-16". the olds also has a small hose running from the front of the intake to the top of the water pump kind of in a "hoop" or "hook" form, not to be confused with the hose in the same area on the pontiacs which was a straight hose that goes to the back of the pump.
back in the late 70's, gm was sued for placing "corporate" engines in everything they had, ie: chevy engines in pontiacs, oldsmobiles and buicks; pontiac 301'2 in olds and pontiacs, etc.
all 3 of these engines: chev 305/350, pont 301/350 and olds 307/350's are completely different and easily distinguished from the other.
the olds i've already explained, the pontiacs have a valley pan under the intake which can easily be seen and the pcv valve plugs in under there in the rear, i believe and the intake can be removed without removing the distributor, and the chevy is, well a chevy.
now, a common change in the 350 diesel cars was to remove the heads and such from the diesel motor, place gas heads, intake, carb and distributor and run them as gas motors. this was done because the diesel heads easily cracked and the diesel 350 was basically a gas motor anyway.
the easy way to tell if the car was a diesel is: 1) the gas gage in the dash would say "diesel fuel only", and 2) by the gas cap it would say "diesel fuel only" and the gas tank opening would be completely open to accept the larger diesel nozzle...and there would be a hookup under the hood for (2) batteries, one on each side of the hood instead of one.
the last choice u have is to take the vin# to ur local gm dealer and they can decode it for you to tell you which engine u have/should have.
good luck and GOD bless.