So, SSH, What is the largest carb that will fit under the 273's air cleaner?
4 5/8" diameter air horn is the opening limit, the largest stock AFB's are roughly 600cfm, most are less.


How difficult is it to find a "real" 273 carb?
Finding one might take some searching

How much would it cost the OP to have you do such a carb?
Or the largest carb mentioned above? I will restore any customer supplied good core AFB to "like new" condition for $399.00. I can also build clones just like my Hemi clones which will have as much as 800 cfm, they are based on new style Edelbrock AVS carb bases with vintage 4 5/8" tops. This way you can still use your original air cleaner, all other stock parts fit as they should, you get a carb that looks and runs as good as a new one and uses readily available modern jets and rods. These are $599.00 plus shipping, built to order.

I am assuming the OP wants it to "look" original, but I don't believe he's talking about looking original to a concours judge. So what's the best way to go to feed that 360 and still keep it looking like a 273 to the casual bystander? The clones I mentioned above

Would it be possible to modify the stock air cleaner base to work with the later larger OD airhorns? Sure, anything can be hacked up, but I wouldn't do that to an original 273 air cleaner