"They'd be little ponies"

Not so. The Italian standard horse (CUNA) is about 2% smaller than a DIN one. Not a significant amount when you are talking about over a hundred of them at a time. SAE net is also in the same ballpark. SAE gross (the scale on which OHV Volvos were originally rated) is the Shetland pony of the bunch. SAE gross is measured with no air filter, alternator or other loads on the engine, and open exhaust. The other three are determined with all accessories in place, as installed in the production car. All of this, of course, becomes irrelevant when one includes dyno measurements of modified engines, which can not be compared directly to 30+ year old factory specs. Unless you test a fresh stock engine ON THE SAME DYNO, it is not a valid comparison.

If you do the math, you will see that two 40DCOE Webers will flow a heck of a lot more air than two SU HS6s: 2 x HS6 = 2 x 1 3/4" = 2 x 44.5 mm = 2 x 13.96 sq. cm. = 27. 92 sq. cm. total area. (leaving out the various obstructions such as the needle, the bridge, the bottom edge of the piston, and the throttle plate edge on, assuming WOT, for purposes of comparison) For the Webers you have 4 x 36 mm venturies = 4 x 11.3 sq. cm. = 45.23 sq. cm. total area. That's nearly double the area of the SUs. Even if you have mistakenly installed 28 mm venturies (you didn't get your Webers off a 1300 cc Alfa, did you?) you still have 35.17 sq. cm. of area---about 1/3 more than the SUs. While I have no figures to back it up, I suspect that the airflow through the Webers is a lot smoother than that of the SUs. The SU has all the restrictions and irregularities mentioned above, whereas the Weber venturi is perfectly round, and the obstructions in the path are nicely faired.

An anecdote: At some time in the late 50s, Lotus was using the 1216 cc Coventry Climax engine, and had spent much R & D time to achieve an output of slightly over 105 HP, with two SUs. They figured this was all the engine was capable of. At a race in Italy, a Weber engineer saw the carburetion setup, and was not impressed. He invited the team to bring a car to the Weber factory and have them see what they could do with it. The ran it on the dyno for a baseline, and got something like 108 hp. Then, with the Webers installed, with guesstimated jetting, the number jumped immediately to 116 hp. After some experimentation and fine tuning, they were able to find several additional horses that had previously been in hiding. The Lotus test driver confirmed that the car was indeed much faster than before, and from that time onward, competition Lotuses used Weber carburetors, or the very similar Dell'Ortos.