DMA,
I'm about to conclude the third year of a one-year restoration of my 1964 Giulia Spider. If this is your first adventure with restoring an Alfa, there are a host of things that you cannot begin to imagine that will require much more time, effort and money regardless of what level of "restoring" you might envision for your car.
You do not mention your location, experience you've had with previous restoration work, or automobile work, in general, and that's your business. In addition to the wealth of incredible advice, information, and entertainment available here on the BB, I would suggest that you click on the 'Forums' tab and scroll down to and check out the International and North American AROC chapters; there may be one (or a member of one) located close to you.
Local Alfa chapters are great places to meet some friendly folks with lots of experience, knowledge, encouragement and elbow grease (if you supply some food and drink) to help with your project. The AROCOK (Tulsa, OK) chapter continues to be a source of all the above and more.
If you are willing to do so, you might post the Spider’s VIN and the engine numbers (photos are always appreciated and helpful) as some members have books or have started registries with data referring to build dates, car model types, what range of engines were probably installed in which cars, but more knowledgeable members can guide you through that maze.
All the best with your project; it will be an exciting, eventful and worthwhile journey and not at all what you expected. The Italians have a wonderful expression: “Non tutte le ciambelle (cham-bay-lay) riescono (ree -es-cono) col buco”, “Not all doughnuts come out with a hole.” In short, “It’s not what you expected, but you’ll enjoy it, just the same!” I’m sure your grandfather would be both pleased and proud.
Ray