not much use i'm afreaid...
i have come across same problem while working od a 1970 spider resto, and have posted several times here and elsewhere seeking body repair manual since measures would be there but haven't found what i need yet. i have such manuals, either n print or as PDF for several other cars, fiat 125, 131, 132, lada, but haven't been able to source one for 124 spider yet.
detailed measures for lada are of some use since it's identical to 124 sedan, and a lot of underside parts are the same, but again...
http://fiatspider.com/f08/viewtopic.php?f=30&t=18904
also, people who actually own spiders have been less than helpfull on this subject since 90% of them are not mechanically inclined and simply do not know how to measure their cars and what to look at. i have been to see three other 124's since i've started this resto and have found, in all three cases, much to owners disbelief, that all three have been previously worked on and didn't line up to any reasonable degree, like door opening being a centimeter shorter on one side than other etc.
alll in all, good luck, and if you do find what you seek please send me a copy too
