Well, I hope so. I have a '65 1600, Ausca spider, like yours, but with GTA running gear. It came from Alfa with the belts pictured below. The forged eyebolts through the floor, have factory welded in reinforcement in the floor pan. Some time ago this was researched here on the BB, and it was found that some of the last Giulia Spider Veloce's had these mounts.
Next, my '65 Ferrari 275 GTB had NO

factory belts, or mounts. Early in my ownership, I raced it, and eventually built a 5 point system, copied from an F40. I replicated the later mounts from a late '67 275 GTB/4. My starting point was a Simpson "latch & link" system that I bought from Pegasus Auto Racing, (wwwPegasusAutoRacing.com) 1-800-688-6946. This also appears period correct, in either of these cars.
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Gordon Raymond
Illinois SNO Alfa Chapter Director
Illinois SNO Ferrari Chapter Director
and sometimes, CONFUSED AND INCORRECT, but Larry helps me out.