A pair of the original "big" (2-15/16" flange) 235 carbs is too much. There is a slightly smaller venturi made for the Gen-3 230" "economy" motor, but not much better. There are even smaller B, but they have a different flange pattern.
If you want to work with these, you may find that the throttle disc is too far below the transition slot and the slot isn't exposed to vacuum at idle. A small chamfer can be filed or ground in the disc’s beveled edge next to the slot.
Very important: the initial spark advance greatly affects idle quality and off-idle response. Try bumping the distributor a bit to see if this helps (if it does, the advance curve will probably need some tinkering).
