Quote "I was hoping I asked a specific enough question without having to go into the often-repeated dissertation of which engine modifications have been done in order to justify our choice of a 2x1 manifold."

Forgive me for bothering you with a question, that had you answered, I could possibly have given a good answer to your first question.

Quote "What carburetors do you recommend that fit the two bolt (3 inch spacing) mounting configuration for a Chevrolet 235?"

Good luck!

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop