Mission 76 - Bust up Santini's Weapon Deals
Both of these objectives are some distance away, so you might take this time to pick up some side missions, or drop by Father James' for a chat. When you're ready, we'll start out with the Southdowns missions- the explosives deal.
This is pretty small operation, and while there's a lot of movement, it's not coordinated to catch intruders. Pick off small fry until you can gun down the rest, then scoop up the goods.
For the second deal, there's a junction box at the nearby switchhouse if you want a better overview of the site. The map tells you to bring a tacvest to this operation, but it's pretty much the same story as the last- keep toward the far side of the train cars (the sentry inside can be shot with a silent weapon), and pick off anyone in luring range. Some guards face the range permanently- a bullet in the back of the head will do if you don't feel like waiting. Clean up the cash but ignore the shooting range itself- there's nothing there. Time to get back to Barclay Mills proper and finish this (Note: sometimes the objective marker will not clear, even after this mission as done. As long as you've done the cash damage to the Racket, don't worry about it).