I have been told that dell parts are still availabe but hard to find, not as common as weber parts. Errol again is a good chance too get Dell parts through or ask the people your buying it through wether they know where to get parts.
Reason not to buy may be that its off a Alfa 2lt and the jets, chokes and correctors may be way off what you want and that these parts are expensive and could cost another $100-300 to get the right set up for your planned motor. I was lucky enough to by my webers off a worked A15 motor.
Also try and find as much info on what condition and history on prior rebuilds etc the carbs might have recevied. Because rebuilds on these carbs arent cheap. Another probelm with sidedraughts (that I have been told) is if they have done lots of Km's and have not been looked after, is that they can get grit and muck build up internally and require them to be drilled to fix the problem which is alot more $$$.
these are just things to think about before buying lemons. but trust me if you get a good deal and get these babies going you wont regret it!!!
cheers