Honestly, a lot of the parts that came with the Gran Sport were pretty basic. Good enough to ride for a while, but not durable. When I bought mine around 1975, I sold a lot of parts back to the shop at the time of sale. I think I only kept the cranks, brakes, and headset. I already had some wheels, pedals, etc. to use, and bought some SunTour Cyclone derailleurs and bits. I rode it that way for 14 years, so no complaints from me!
If the frame is in good shape, no reason not to upgrade the bits.
Steve in Peoria