Even though 55-56-57 Chevy Clutch Pedals use the same replacement part number (3735587), there are slight differences, in the production parts.
Below I have a couple of used OEM assemblies to use for comparison.
 |  |
| 55-56 | 57 |
The 1955 and 1956 Pedals, use unique wire clips for their return spring attachment and their own return spring bracket,
attached by 3/8"-16 bolts screwed directly into threaded holes in the pedals.
While in 1957 Chevrolet switched to a wire hook on one end, with an oval
plate hooked to a pin on the spring bracket on the other.
The spring bracket is attached by 3/8"-16 bolts with nuts and lock washers. The pedals have "thru holes".
The 57 spring bracket doubles as the pedal stop and is mounted on the inside of the pedal.

The 1955-56 Pedal assembly used a separate
Clutch pedal stop bracket part # 3709581 and
Two different rubber bumpers depending on whether
you had power brakes or not.