The first option is to get the original Dell'Orto Carbs operating as well as they can. Many carbs are worn from decades of use and may have been severely damaged by corrosion from long periods of inactivity. It is not a simple job to get them back to as-new condition and it may be cheaper and better to simply replace rather than rebuild. PHF's (with the later male spigot type mounting) are available new for about 160GBP (for example 32mm here, 36mm here), which is possibly less than you'd spend on jets, slides and kits alone. Well worth checking out before you throw time and money down a bottomless pit of frustration.

If rebuilding, strip to their component parts and ultrasonic clean the carb bodies. This helps (but is not certain) to remove crud from the small idle circuit passages. Rebuild kits containing all the required o-rings and gaskets are available from most Italian bike shops.
Note the condition of slides and carb body bores, needles and needle jets, choke plungers, accelerator pump diaphragms and the shafts/bushes at the top of the carbs on a triple. These all wear and contribute to poor running, but all can be replaced or renewed.

Gregory Bender has compiled a lot of Dellorto information including parts diagrams, tuning guide etc here.

Dellorto PHF Rack
Image courtesy of Bevelheaven - an excellent source of parts BTW.