tar=>creosote?
it might be a good idea but i m not sure if that building has module slots to begin with
yes the tar processing unit has module slots, also sand casting is done in same building (add please)
from tar make's creosote and from creosote make's sand casting
just first 2 have modules ( so mostly early game)
i will add creosote but castings not ( you need very few of them to gigin with and it might crow off balance other stuff too)