I'm always amazed when I see those old pics too. Yup, EXTREME body roll on SKINNY tires. ......... and yet, in their time, they clearly kicked butt. Good drivers without a doubt but I believe there were other things at play also.
1. Extreme light weight. FIA 289's were around 1900 lbs. When was the last time you saw anyone with a replica that was that light? Pretty rare, and often the replicas are 2500 or higher, with FFR being among the lightest (2200 maybe?).
2. Competiton cars in that era were similiar and often WORSE in the handling department. Certainly Vettes (WAY heavy by the way) did NOT have "great suspension" at that time.
Footnote to #2: Shelby didn't just "stumble" over the AC. He KNEW that car all ready had a decent "track record". For the time it's suspension was quite advanced.
3. Superior brakes. The Vettes of that era did not get disc brakes and IRS until many years AFTER the AC all ready had those advantages.
For the time, it was a first class car to go racing in!
So how would it stack up today, with modern tires, brakes etc? Not that bad as it turns out! STILL a worthy competitor.
How hopeless the first 260-289 cars were! Clearly NOT yet ready for prime time in SO many ways. But what a great place to "start".
Ernie