carburetor differences?
 

Hey guys I'm trying to sell my carb, I paid $800 for it off of summtracing a year ago heres the link
http://www.summitracing.com/parts/igs-ng1019

Now I have it listed for $500. There is a gentlemen interested in but he shows me this link
51 Carb. Only

Now whats the difference? They have different part numbers, I have googled each part number and they come up with around the same price for each part number but not a single site has both part numbers or very much description of each carb. so whats the difference between the two why is one 400 and one 800?
thanks for the help

Product description

"These Inglese EMPI carburetors are cast from Weber-type die-cast tooling and feature design improvements and tighter final tolerances over classic Weber IDA carburetors, making them viable options to the original. They are designed for a wide variety of Inglese and other intake manifolds and can be ordered individually or as part of an Inglese induction system for an easy "bolt-on and go" installation. Any engine that is compatible with the standard Weber IDA carburetors will accept the EMPI carbs and use all of the same mounting points and linkages. For anyone looking to increase the flow rate of their engine without a big price increase or simply to replace the carb on their current Weber-fed engine, these Inglese EMPI carburetors are a great way to go. "