A man of historic proportions, named Brad Artigue (pronouced R-teeg, or so he tells me), has compiled most of the information you need.
first get the pdf labeled "FIAT 124 Spider Engine Maintenance and Modification" to help determine exactly which carb you have. you probably have the stock carb (The 75 was a good year!- 32adfa), but you wouldn't be the first with something different.
Then scroll down and there is a list of weber carb diagrams. Pick the one you have. all else fails I have the 32adfa and I spent a looooong time looking at diagrams, etc trying to figure the stupid thing out, so I can probably help.