Grandis didn't make a ton of different models, especially in the 70's. I would say mid-70's sounds right, given the frame details. It has the G's in the side of the headlugs like the one on CR, but the three-pronged Grandis thingy on the fork crown like this earlier Super Leggera:
http://sports.webshots.com/album/560084442lIIhii
Yours has a crown more like the earlier bike - which also has those trick top tube braze-on cable guides.
This Super Leggera is clearly later:
http://www.wooljersey.com/gallery/v/...sSuperLeggera/
I'm assuming yours has the curved brake bridge, though the photos don't show. I'd guess circa 1974-5. Probably a top model - i.e. "Special" - built with SL, but without the degree of detail given to the Super Leggera.