I used a dremel tool to grind/extend out the recess in the trigger guard fitting and to cut out the mag well. The marllin trigger guard extends about an inch and a half past the ATI recess provided. And be very careful with that marlin trigger guard, it is plastic and is a little flimsy around the edges. I really like the ATI stock, it's nice and sturdy in case you need to buttstroke something.
Hope this helps