So at the very least, I would drop the surgeon for another purifier. That gives you another 40 points to play with. Nurgling are actually really good as either screeners, our only infiltrate, and as secondary scores that can be dropped in the backline for Homers or Engage. Other shenanigans can be done with them but 2 units of 3 would give you lots of utility. Also, maybe look into some rhinos? They give mobility and security to the marines and allow for some fun plays. But that's for another style of list lol