I do not know what might be commercially available today.
85 years ago, these were available from Carter:
[img]
http://www.thecarburetorshop.com/Carter_adapters.jpg[/img]
Any of these, with the exception of 72-32, can easily be reproduced:
(1) identify the flange size(s) needed
(2) acquire 2 worthless carbs at a swap meet or junkyard (Rochester B's pretty well fit this category
) with the correct flange. Others that fit the category are Carter BBR, and Holley 1904. You might even use a Carter YF that has been stored at the bottom of a pond.
(3) place the cast iron throttle bodies in a power hacksaw, and cut the throttle body just below the throttle shaft.
(4) orient the the cut off flanges in the necessary orientation (straight, cross, etc.) and weld together.
Jon.
