We just finished up the Two Man Band league's latest round, and I went 122-40 with Ed Morris and George Davis filling every role.
I started 1885 and '86 Morris in every game until the finale just for a rest break, and both of them won 54 games. I realize it's a far cry from a record for one pitcher, but I wonder if anyone's seen a pair of 50+ win starters on the same team.
https://www.whatifsports.com/mlb-l/playerstats.asp?teamid=1475423<id=0