Holley has made numerous fresh runs of the classic muscle car carbs over the years, including many with no date stamp on the choke air horn, to be "dated" by the reseller. Most are technically correct to the original internal specs, although some of the later ones have been altered for emissions; for instance, the most recent re-run of the LIST 2818 and 2818-1 (4150) carbs (originally used on the '64-'65 Corvette 327/365 and 327/350 engines) changed the primary metering block internals such that the distributor vacuum port on the passenger side supplies "ported" vacuum, where the originals supplied full manifold vacuum from that port.
The most obvious clue on the re-issue carbs is the hex-head float bowl screws, where the originals used slotted and beveled float bowl screws.
