Thanks for the pictures ( a picture is worth it thousand words!

)
Personally, all I can say is it looks to be a 41/120 three treble reed (LMH), five bass reed accordion which is probably from the late 1950s-early 1960s from their "pro" range. The reeds are possibly hand made.

The "Magi-Colour Tone" coupler gives you the "LH" coupling ( often called "Organ", elsewhere) which may have been intended for playing the kind of jazz played on accordion in the day.

Since it has the standard set of keys and buttons, I can't imagine why they'd call it the "Gigante".

It's been well used (showing signs of wear) , but not abused.
I'm sure someone here will know a lot more about it (including the likely type of reeds installed).

What is the other accordion you're planning to sell?

Here's a link to a 2018 thread on a similar instrument (with comments by our member JimD, very knowledgeable concerning Sonolas such as these


)
See here:
Hi everyone! First time poster here. We recently bought a Sonola AA3 of a street vendor in Baltimore for $40 because we liked the look of it and thought it was kind of cool. We didnt know what it was when we bought it, just though it would be fun to maybe fix it up and try it out. Wife and I...
www.accordionists.info