My 340 getting 6 mpg
Even 100% stock 71 & up 340's used a 750 TQ. Maybe Mopar had it wrong.
800 cfm was the smaller TQ. (maybe a Carter fib on the size) A properly tuned air valve on the secondaries will give all the air the engine demands. Some 360's came with an 850cfm. IIRC the Mopar Q-jets were 725 to 750. Triple boosters on the primaries. I pulled a nice one off a 318 van. It did better on the MPG than my TQ. They have air valve controlled secondaries too.
Properly set up you could probably run a 850 TQ slant if you tweaked it enough.
I have a bunch of TQ's. I collect the jets and metering rods out of the emission ones. Several '77400HP auto models. I have a Strip Kit too. (no, I don't want to sell it!)
I have a "Doc Fiberglass" Electric Banana secondary spring adjuster tool too.
Every used TQ, BBD, AVS, AFB, and Qjet I have need to have the throttle shafts bushed.