Go for Solexes on a road car, they have a vacuum port so you will at least get some fuel economy.

Webers and Dellortos both have their ups and downs, if you get the 2lt alfa dellortos you will have trouble getting them tuned at 1/3 throttle as they have a lot of progresion holes meaning a rich mixture and leaning it out by running smaller idles can cause significant engine damage. You'll have trouble finding a proper pair of universal dellortos. Parts are plentiful through an Alfa bloke on ebay, I have bought kits and jets through him before.

Ive never seen a 42 dellorto.

I have 42 webers on the racecar and they are perfect for a worked L16. I dont think you'll need to go to 42's for an A-series donk, the money you would have to throw at the thing to make 42's work will not be worth it and not streetable what so ever, trust me race engines belong on the track not on the road, they like to rev and not idle, you'll be going through plugs all the time. Get some new 40's, nice cam and clean up the ports freshen head, rebuild the bottom end and get it dyno'd with someone who actaully knows webers and you'll be set.