My opinion is that 4 SU's would be a monster to keep in tune. I know that some of the pre WW2 Rileys tried it out with some success, but then again, there are some Brits that will try anything.

The facts are that SU's/Hitachi's/Stromberg CD are all Carbs that rely on the "constant depression" type which is an auto engineers way of saying constant pressure drop across the Carb. In fact this rarely happens in practice but the piston can usually react pretty quickly. They are not like Bike Carbies ( Amal, Dell'Orto etc) in that in these carbs, the slide (or piston) acts as the flow controller as opposed to a butterfly in the SU type.
If you are looking to go down this path, have a look at some of the 1000 to 1200 cc in line bike engines. I reckon some of their set ups could be adapted and would probably work quite well. I know of at least one Sprite (a few years back) using 2 X 1-1/4" GP Amals that went like the clappers