That is not true. We had modified Rochester 2bbl, 4bbl with PWM controlled metering rods that were able to go closed loop for the 14.7:1 AFR. They were used from 1980 until TBI.
The directive from Engineering Staff and Milford Proving Ground was that carbs would not have adequate driveability with overdrive transmissions. Those with tall diff ratios would not work at all. Something like a 4.10 diff you could get away with it, but only with expert carb tuning and no closed loop. Couldn't meet emissions.
Hmm!
I have a 1994 350 Ex-TBI engine in a Suburban 4x4 , 670 Holley now sitting on a Performer intake, ignition switch to straight HEI. A 700R4 now resides behind the engine pulling 3.55 gears.
The only other change to the engine was a better cam. Ditched the crappy factory emissions cam to one with a little more lift and duration, not much. Still currently have the crappy heads on that project. It is pending a 6.0 LS swap!
One needs to remember that the early TBI truck engines were only rated at 210hp. In reality at the wheels comes out to maybe 165hp. in factory trim. The cams sucked and the cylinder heads sucked even more to meet emissions. We did find on a buddies 1990 that a 500 cfm 2bbl Holley did very well with good throttle response.
So there are many factors that come in to play and how much you want to play with the old emissions engine and what state you live in.
But if you have the 4L60E without a stand alone tcm with the elimination of the TBI system, you are on borrowed time.
Swap to a 700R4 (or non-E 4L60) like I did or get a stand alone TCM!
Greeting from South Central Texas.