Refactoring to patterns by Joshua Kerievsky might help. It’s not the best book (Refactoring by Martin Fowler us another), but it might help with planning the wo

Refactoring to patterns by Joshua Kerievsky might help. It’s not the best book (Refactoring by Martin Fowler us another), but it might help with planning the work. Quantifying cost and writing up a proposal then at least based on a defensible foundation.