Thought I would share that I finished my first session in a new campaign with my son and three of his friends.  Since I haven't had a chance to pick up Rats in the Walls yet, I went with Tomb of the Iron God by Matt Finch, which I got from the OSR Bundle of Holding.
First thing I changed was replacing all reference to goblins to orcs.  It's a slight power jump (1d6 HD to 1d8 HD), but the one wandering encounter was a group of 1d6 orcs and the group handled them well.  I placed the ruined monastery over the tomb one hex (24 miles) to the northeast (?) of Khromarium (towards Stonebrook).  I started the characters in Khromarium already "familiar" with one another (easier than "you all meet in the inn" trope).  They only explored 4 rooms, but managed to wipe out the aforementioned wandering orcs.  However, the barbarian almost met his match with the grey ooze, falling to -8 hp before being stabilized by the cleric.  After that, the party decided to return to Khromarium before exploring further.
I'll post more details about the characters somewhere else.