The only song I know where Biggie mentions 2Pac is "Can I get wit cha" .
There's 1 line that says "...upside down, my name ain't Tupac, I don't get around...".
Not a real diss tho...
But maybe it could be a diss, perhaps Biggie said this shit ironically, in a way that no other person aint that cool like Pac... maaaan, who knows ??