Yes, that's quite a jump up, and will have idle tip-in and response problems.
What sort of power system do they have?
Ball & Ball carbs have a mechanical accelerator pump that is adjustable based on where a pull rod is attached (controlling the length of travel - pump stroke). This is good for a dual carb setup because it doesn't depend on vacuum.
But to panic's point about a jump: Hollander Interchange shows the original equipment to be a number 11 flange:
Hollander number 11E - which is a Stromberg EXV-2 which has a 1.25" flange. Your 1.5" flange is Hollander number 21 - used on Dodge trucks (21W). Just one is a 44% increase in throttle area:
flange . . . . .radius . . . .r2 . . . . . .area
1.25 . . . . . .0.625 . . . . 0.390625 . . 1.22718463 +44% throttle area
1.5 . . . . . . 0.75 . . . . . 0.5625 . . . . 1.767145868 +0.539961237 sq inch delta
There was also 1 3/8" flange B&B used on Desoto - but that is still 21% increase in just one carb.
When going to a dual one needs to fit carbs that are smaller then the original . . . and/or make engine mods that increase the CFM demands over stock specs.
