Just found this in a different group...
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There are many ways to tell if it's an original, wish there were more pictures.
Telltales of original from this one picture:
Location of gas filler is MUCH closer to rear hood edge than replicas.
Flatness of cowl and windshield at base. It appears there are wiper holes, but I can't see the linkage/stubs.
Headlight adjustment screws at 9 and 12 o'clock.
"It wasn’t until I saw my first Porsche 550 Spyder in the flesh, 550-0056 at the 50th anniversary for Porsche in Melbourne, Australia that I knew I had found my dream car. It was at that moment that I realised all future models produced by Porsche had evolved from this one purpose-built race car."
Even though I went the plexiglass race windshield route myself. If I recall in my research for my Spyder build at least a few (550-004, 005, 006) all had speedster windshields to begin with. A few of them also had wipers. The only thing consistent about spyders are their inconsistencies based on previous owner preference and time. With the exception of the gas tank filler location it seems all other bets are off even then a few covered the filler with a bubble for aerodynamics.
My eye is drawn to the filler location, workable latches, firewall (even then some have been modified), and the front wheel well where the fiberglass tub meets the inside of the well. You get those right and people will second guess themselves