1 of the carbs on the chevy 6 should have no choke and the idle circut removed/ blocked off, if it is not, you will get this. no new carb is going to fit on the intake manifold without an adaptor. you could go to www.stoveboltengineco.com and get 2 of his 1-2bbl adaptor's and 2 of the Holley/ Webber 5200's he sells, he will be able to tell you what to do to them to get them to run on a dual carb setup. they work nice on Chevy 6's, that's why he sells them