I run 1:1 on the two Ed 600s on the 302. Granted it's not so much a putt-putt show grounder - 4000 stall converter, 4:11 locker or 4:56 spool depending on mood, locked timing at 36. However, the Ed primaries have smaller bores and more efficient boosters than a box stock 1850 so considering the motor as two 4 cylinder engines you could run a vacuum secondary unit on a 4 banger no problem. The 1850s might be a little more sensitive to the car setup because the primary bores are larger and the boosters less efficient. But on a dual plane, remember that the engine sees about half of the carb size at any particular time. If you are running vacuum secondaries, those are not even in the picture. Now we've gone from "1200 CFM!" to more like 600 and on a dual plane around 350 for any particular intake valve that needs some juice. And that's with the pedal floored, not just driving down the street. You'd not have a problem with 600 DP on a 390, 351 or even a 302 so a 1:1 with a pair of 600 VSs is not much of a leap.
If the car is low gear (3:25, 3:50) with a tight 11" street converter you may have to play with progressive to get the tip-in performance you think you like. With a high stall converter still building heat while you're cruising at 3400 RPM/55 MPH you really don't care so much about "tip-in" LOL.
660s are 1:1 internal and the other DPs use a progressive link between primary and secondary so running those is another thing entirely.
