What are some of the go to sling mounts when using a MAG401 buttstock? TIA!

I would just thread it through one of the 2 slots that are built into the stock and then back through a tri-glide. Both positions can work it is just a matter of preference. Another option is butt plate QD swivel point before the stock. Some people like this position I prefer QD on the stock or through factory slots.

Here is a good video on 2 point sling installation. I also recommend the VTAC sling. I have one and a Vickers Blue force and prefer the VTAC. Both are excellent and will serve you well. Don't buy cheap slings.