Note that the cup threading isn't the only difference between italian and english bottom brackets, the shell width (68mm vs 70mm) is also a difference, so you'd need an english spindle to go with your italian cups and newly-tapped italian bottom-bracket shell.
It would cost, imho, a lot more to tap out the shell (i'm guessing $25-$40) than it would cost to buy a new set of shiny Sugino (on topic) bottom bracket cups, similar to campy, english threaded :
http://harriscyclery.net/
In my opinion, you should not tap out a bottom bracket for the larger (Italian) threading until the bottom bracket has become stripped.
Conservative frame management is best. You should not make the frame fit the parts, you should try to keep the frame original and get parts that fit the frame. User new-tech bargain-basement parts until you can find the right vintage parts.
Best Wishes,
- Don Gillies
San Diego, CA, USA