The Summit carb is a redo of the old Ford 4100 four barrel that came out about the same time as the Holley end bowl carb in 1957 to augment production rates that Holley couldn't keep up with. This thing became an Autolite and then Motorcraft item after Ford was forced by Federal court to divest its holdings in Autolite. It was used in production from 1957 through 1969 in several sizes on the Y block in 57, the FE's and MELs, and the Windsor engines through 69.

The version Holley made and sold, then Summit have had some modifications made since the Ford days such as centering the float pivot in the bowl, using an external fuel supply for the front and rear bowls, removing the secondary vacuum actuation diaphragm from integrated with the rear float bowl casting replacing it with a Holley style side mount. It retains the very nice removable annular booster cluster and the trash prone position of the main jets and power valve on the bottom of the float bowls. These use standard Holley parts just in a different position, unfortunately this position does collect junk that comes in with the fuel, but today's better filtration should cure much of that.

Here's some history the first picture at the bottom is the original 4100
http://www.cometeastcarclub.org/autolitecarbs.html

Here's an article on the Holley version, he gets his history about this thing wrong.
http://www.fordmuscleforums.com/ind...-road-test.html

It's actually a decent carb; many millions were out there in through the 1960's. From a hot rodders stand point it’s not as easy to work on as the Holley simply because the power valve is only accessible by removing the carb from the engine 'cause its housing is on the underside of the primary float bowl. For a racer this would be real PIA but for a set and forget street engine this is not a problem.

All-in-all, this is a decent carb that will do anything the equivalent Holley will do and with those annular boosters show a little better gas mileage doing it.