Here's a shot of my ERA FIA:
Note that it has the windshield laid-back like most of the original FIA's did.
I think the windshield angle and racing windscreen are giving you an optical illusion that the body is different. The FIA and USRRC bodies are the same - there are detail differences like the trunk dimples and windscreen, and several iterations of lower
oil cooler scoop, but, most of the metal is the same. They both look more agressive than a slab-side due to the flares,
oil cooler scoop, and windshleld angle.
If you send me an e-mail, I'd be happy to send you more pictures of my car from different angles, if that will help. The ERA FIA body is quite accurate, and was detailed off of Mike Shoen's CSX2345 - the only FIA still running around in it's original sheet metal.
regards,
Jeff