Interesting, we say "If my grandma had wheels she would've been a wheelbarrow!" ( "Se mia nonna aveva le ruote sarebbe una carriola" ). And there's also the version with grandad, but it's better you look that one on Google "Se mio nonno aveva..."
We (neighbours to the east) sometimes say “If my grandmother had balls, she'd be my grandpa” as a meta on the other versions of the grandma jokes, but I searched and did like the Italian grandpa version.