That's where Clemenza coached Mike for the Solozzo/McClusky hit ...
(well not really, in the book it was Clemenza's basement, but what the heck ..... /laughs)
I’ve re-read the book recently, but you’re way ahead of me on that.
If you look up the address on the realty sites, look at the kitchen shots. Can’t you just hear Clemenza teaching Michael to make spaghetti for a bunch of mob soldiers?