If you want performance from your Dell'orto without the mods then a 3.5" manifold and Lynx filter would be a good option, followed by a Dyno setup to get the jets right.
My Dell'orto is on a lynx manifold that defines the term swan neck! It has no flow characteristics at all - the fuel just 'drops' down into the inlet ports!! It isn't jetted perfectly yet, the manifold sucks, but it still goes hard and sounds simply awesome! Shame about the increased fuel consumption though, I've only had it on for two weeks and I've run out of petrol twice!
Much as I like SUs, I purchased my Dell'orto after repeating issues getting my HS4 to work properly. Too much fiddling with needles, oil and springs got the better of me. As a matter of fact, the HS4 went faster at high RPM, but drivability was crap, so you could only drive it 4000-6000 rpm. The Dell'orto spins the wheels much better
Anto.