IF you're referring to the casting numbers, the left side is 3989343 and the right side is 3989310. Hope this helps. I placed an ad in the wanted section for these exact pieces and the responses I've received have been for high dollar parts. Don't get me wrong, these replies are appreciated, but I don't need the manifolds that bad.
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69 SS396 69 Malibu Ragtop
70 Monte 72 El Camino
Team Chevelle Gold #33
ACES Member #02913
Chevelle Club of Michigan
Rode shotgun in the ONLY Z16 convertible made.