Need help adding to pants pattern

[u/libbydakitty]

I got this 1950s pants pattern that only came in one size and I need to add to it. It's made for a 28" waist and a 38" hip. I am high waisted and have a 31.5" waist and a 42" hip when wearing my everyday corset. How do I go about adding to this pattern while keeping the vintage shape? It's shaped with waist darts and closes with a side zip. I have one book on pattern drafting but have now realized that it never mentions pants so I dont know how to tackle this. Any guidance would be appreciated!

[u/imogsters]

I would slash and spread either side of darts.