It looks like there are a few different versions of the Holley 1940. Ron (
rjseibenick ) at Ford Six is a Tempo racer, and he's measured his 1940 as being a 1.352" venturi carb, although I'm sure that is not the stock venturi diameter for the #R 4529 144/170/200 replacements
If some versions have a larger venturi than the 1946, and the flow rate is 202 cfm as a 1945, and, according to Ron at Ford Six, a 212 cfm rating as a 1940 with a 1.352" venturi.
See link
https://fordsix.com/viewtopic.php?f=11&t=11031
And the Holley carburetors and manifolds book.
ISBN 0-89586-433-9
http://ecx.images-amazon.com/images/I/51zR2yBC85L.Image._.jpg
Be aware that there are 26 historic Part Number listings of the Holley 1940.Some are generic, non Ford Std parts, others are full Autolite/Motorcraft listings with a Ford basic part number (BPN) with a letter suffix, and with that tag, you can find with 100% certainty that are carb is a big or little item.
I'll bet the 212 CFM ratings with the 1.352" venturi on 250, 240, 300 and older I block 223 and 262's
won't be the same as the generic 144/170/200 item.
It is a big 223/262/240/250 or 300 carb if its PN coded:
R 4454-AAS
R 4468 AAS
R 4509 AAS
R 4520 AAS, additional BPN plate suffix A
R 4522 AAS, additional BPN plate suffix C
R 4523 AAS, additional BPN plate suffix D
R 4524 AAS, additional BPN plate suffix E
R 4525 AAS, additional BPN plate suffix F
R 4526 AAS, additional BPN plate suffix G
R 4527 AAS, additional BPN plate suffix H
R 4528 AAS, additional BPN plate suffix J
R 4536 AAS, additional BPN plate suffix Y (an early 223 replacement)
R 4537 AAS, additional BPN plate suffix Z (an early 262 replacement)
R 4692 AAA
R 4696 AAA
It's the little 144/170/200 stand in item if its PN coded as one of the following:-
R 4529 AAS, additional BPN plate suffix K
R 4530 AAS, additional BPN plate suffix L
R 4531 AAS, additional BPN plate suffix M
R 4532 AAS, additional BPN plate suffix N
R 4533 AAS, additional BPN plate suffix R
R 4535 AAS, additional BPN plate suffix T
R 4693 AAA
R 4694 AAA
R 4695 AAA
R 4697 AAA
R 4701 AAA
The listings for doubting Tom Co's, um Thomas'
3 listings
http://www.tocmp.com/manuals/Carbs/Holley/MasterList/index30.html
16 listings
http://www.tocmp.com/manuals/Carbs/Holley/MasterList/index31.html
7 lisings
http://www.tocmp.com/manuals/Carbs/Holley/MasterList/index32.html