Ta Norm.
That one is the earliest of the trio; the LHS opening was used on the 1964-66 Corvette 2 Model 523 and 533; and the RHS opening on the 1966-68 Corvette 2 Models 535 and 545, and the 1967-68 Corvette 2 160cc Model 543. Going by the Green Book images, anyway.
The left hand one would be 1971-73; it has the Series 70 MkI engine, the first Vette to use the 'box' muffler rather than a 'torpedo' style.
Here's a pic of an early one with its cover plate:
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