If you had your original engine then the normal , yr, make , model , engine size, trans model or by VIN , catalog application would work. Unfortunately when you did an exchange rebuild you removed one part of an equal equation.
Unless you verify by part number and visual confirmation, your " will fit, it's the same " . Might not be exactly the same.
As you found out, GM gave you the right part number, your engine has a different part number crank.
So like an engine swap, it's a mix and match. Fortunately with GM there is combo that's works, just a matter of " this one ? Nope, next ".