swap in a olds350. (1968) into a 1987 grandprix with chevy 305 W700 4 speed auto transmission
This is a bad idea as you will not be able to pass smog inspection with an old motor.
the answer I was searching 4 was probability and procedure. tech answers not opinions, just the mechanics of the swap please. thanks still looking 4 answers.
With both engines being GM it could be a mostly bolt in change with the right combination of parts but don't count on it. It will cost you far more than just buying a crate engine to bolt in in any case. Remove the old engine and trial fit the even older engine to see how it fits if you are determined to go through with it.
There are differences between the engines although I believe it will be mostly small stuff. Things like dipstick location, manifolds and accessory mounting and brackets. Also I think the Olds engine is a bit wider. Measure outside to outside width at the valve covers to be sure, then look in the car to make sure there are no clearance issues. It's probably do-able but the small stuff mentioned above may drive you to frustration.
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