Castrol 20W-50 is what I use in our '84 Spider, also.
Be careful NOT to use oils described as 'Energy Conserving' (look for a starburst symbol on the label). Those oils will likely have markedly reduced levels of zinc compunds that our older engines require.
Maybe I'm sounding a bit harsh, but you say your "Alfa mechanic" put in 10W-30? He's no Alfa mechanic in my book, unless he cut his teeth on Alfas in Alaska, perhaps.
10W-30 has NO place in an Alfa engine, IMO, unless your driving in the dead of winter in Buffalo, NY.
Drain that stuff and put in at least a 10W-50, or 20W-50 for summer use. A good synthetic like Castrol Syntec or Mobil 1 will provide residual lubrication film to the bearing surfaces even with the engine at rest.