The Offy's flange is not open like the Clifford. I has four holes like the adapter. I have an Offy that someone crudely cut out the four holes to make it open. I'm going to clean up the hack work and use a MrGasket adapter so I can run a 2300 series Holley.
I don't know of any problems with the cast iron 2bbl intakes, it's the exhaust manifolds that have cracking and warping problems. Ebay 2bbl intakes go for $50-$90. There has been at least one over $100. That's insanity! If I needed one, $25 tops is all I'd give. I have two laying around my shop, maybe I need to ebay them
.The best 2bbl intakes were the MP 1piece aluminum versions on the Super Six. They give no real HP advantage, and you are stuck with the small BBD, but they do take off 15-20lbs of front end weight. Used is the only way to get them now, it's doubtful any are still on the shelves.