Found one! It's on the way to me at the moment. Thanks for the search and the offer to send it to me!
Two carburetors on an inline six is either one too many or one not enough. The 300 cubic inch Frankenstein Chevy 261 I'm building will probably run three side draft Keihin carbs for a Harley Davidson EVO engine on home-brewed adapters, to run one carb for each intake port in the cylinder head. Since only one cylinder at a time is supplied by each port, there's the equivalent of a carb with enough CFM volume and jetted for each individual cylinder.
Before you remove that 4 BBL intake, try adapting a Quadrajet calibrated for something like a mid-1980s Chevy 305 or a 307 Olds V8 to it. The spring loaded flap valve at the top of the air horn will prevent getting overcarbureted, even when those huge secondary throttles are open, and the 3-stack venturis in those tiny primary barrels will do an excellent job of fuel metering at any engine speed from idle to cruise speed, far better than the Edelbrock can attempt to do.
Jerry
Two carbs seems to work OK for me on a 300 ci. Better than any 4V I've tried.
