Dean Martin's Volare

I'm trying to learn Dean Martin's vocal melody from Volare on mandolin. My sister asked me to play it at her wedding because it was one of my grandmother's favorite song. I'm pretty sure I have it mostly figured out, but the section where he drops to a lower octave and sings "Penso che un sogno così non ritorni mai più" has me stuck. Any help would be greatly appreciated.

This is what I have so far, then there is the brief section I'm having trouble figuring out, then this basically repeats.

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42--42-20-----20-0--0--020-0-0-020----0---0---0---0-20------------02--02-02--020-0
---4-------2-26-----4--6-------4-6-----46--46--46--46----6246246-6---6---6---6----6-
-----------------------------------------------------------------------------------------------

----------------------------------------------------------------
---0---0---0----0-----42--42-20-----20-0--0--020-0-0-020
46--46--35--35--532---4-------2-26-----4--6-------4-6---- ?
-----------------------------------------------------------------

Great tune. You've made a good start here with the chorus, in A major. The other section is the verse, and it'll start on low C# (sixth fret on the G strings). First phrase goes:

C#-C#-C#-|C#-C#-C#-| C#-C#-C#-|E-D-C#-|B

Then the same phrase one scale step lower (starting on B). Then a similar phrase starting on the open A.

A-A-A-| B-B-B-| G#-G#-G#-| A-A-A-| F#-F#

Then much the same, a step higher:

B-B-B-| C#-C#-C#-| A-A-A-| A-G#-A-| B-B

Then back to the chorus. So the song uses only A scale notes, from low A up to the C# on the A strings. The more you play through the scale, the easier it'll be to pick out tunes by ear.

Will someone be playing the chords with you at the wedding? Anyone singing the words? Have fun with it!

(While I'm at it, I'll recommend the classic hit version by Domenico Modugno. Different key, unfortunately.)

https://www.youtube.com/watch?v=vRF5zSczYEs

Carlo Aonzo plays an instrumental version on his Mandoitaly CD.

Thanks for the help. The wedding is in September, so there is time to change plans once I get it down well enough to play for my sister. Right now, the plan is just me playing the melody and not singing since I'm not a good singer. Now that you suggested it, it would be nice to have my other sister play the chords on piano backing me playing the melody.