· Trained (ex)Professional, , 1953-2018 RIP
The engine number indicates that it is correct for a 1969 US version 1750. Lacking documentation from Alfa, which I have not seen for cars from this time period listing engine numbers to chassis numbers, one can not be absolutely certain this is the original factory fitted engine. However, for all intents and purposes, I'd consider it original.
My hat is off to you for your desire to save this very savable Alfa!! And it warms my heart knowing that some of the parts I saved from my first Alfa, a 69 US 1750 GTV, will once again live in yours.