Going to sell my "beloved" 1976 124 Spider and wonder if anyone can direct me to a reliable resource to determine its value. Thank-you in advance.

I own a couple of classic MGs - 1932 and 1979 respectively, and it seems that trying to get a value on any classic is rather subjective; your best be would most likely be seeing who is selling a similar machine and for how much.

If the right person comes along that really, really wants that particular car, it sells in an instant. If not then you have to perhaps drop your asking price.
The only worry is when it gets snapped up in an instant, and leaves you wondering if you had valued it too low!
Why not 'test' the market with a realistic price that is perhaps a bit too high, then haggle, or otherwise gradually reduce the price. At least doing it that way might help guage how much interest there is in general.

Try looking here:
https://www.postwarclassic.com/?_ga=2.268804018.275409115.1598432561-1303188367.1598432561

(I've used the Pre-war 'sister' site to that one and had good luck)

The UK magazine Classic & Sportscar used to publish values of various models at the back of the magazine, until prices went crazy again a few years ago...

Which I guess means it's probably a good time to sell, if you can bear to part with her

A US publication might do similar? Worth flicking through a few classic car magazines (or the online equivalent) to see if any 124 Spiders pop up in similar condition in any adverts.

Is this any help?
https://www.124spider.org/


And another
https://www.fiatspider.de/worldwide-spider-register