1957 Fuel Meter Covers are unique. The first design has a large sprue on the rear near of the cover. The second design does not have this large sprew. The left side of the cover has a fuel line tap into the pump inlet. The pylon under the diaphram is missing, there are no vent holes, and there was not an anti-siphon valve on the side of the fuel meter cover.
1958 - 1964E Fuel Pump Cover
1958 to 1964E Fuel Meter Covers have a number of improvements over the '57 second design. A vent hole is added, the left side fuel tap is not drilled, the pylon was added and the anti-siphon valve was added - a most important feature.
1964L - 1965 Fuel Pump Cover
1965 Fuel Meter Covers are unique. A much larger starting fuel bypass line was added to the system. The late '64 and all '65 units had a bypass solenoid that alowed main fuel pump pressure to be aplied to the spider.