I'd guess that an "Autolite Spread Bore" carburetor would be an Autolite 4300 unit. IIRC those were designed by GM (Rochester) as an emissions carb.
I had the Autolite 4300 spread-bore on my 1970 351C 4V, they were also used on the 460's.
The carb and aluminum intake ( Boss 351 C part ) were setup and matched, carb flowed in the Ford dyno lab using a Crane Fireball cam back in 1975.
This involved changing the profile of the secondary metering rods.
I could roll into the throttle beginning @ 2,500 RPM and it never bogged or stumbled, you just would hear a deep rumble thru the shaker hood scoop,
and when the cam came on @ 3,200 RPM the big intake ports of the 4V heads started to pick up velocity the engine wound up quickly to 6,200 RPM.
of course the 4:11 rear helped get going quickly. I could stay in front of 427 Vett's thru the 1st 3 gears, but cubic inches eventually win!
With the competition suspension, Koni's at all 4 corners and the G60 radial T/A's and manual steering it was a great handling car with plenty of GO.
regards,
jim p