Alternate way to mount a Century Heavy Bag Mount??

[NewToThisWorld]

Maybe some of guys can help me with this...I bought the Century Wall mount and the holes on it are for 16"s apart while the studs in my garage are 14"s apart...
I was wondering if the solution I've came up with in the link/attachment would work?
Pretty much im mounting the bag mount to 2 3x6 boards and mounting the 3x6 boards to the studs using the M8 lag screws in the picture. Would this securely hold the bag up or should I use different screws/boards etc....thanks

also...I'd just noticed that on the Century Wall Mount box that the mount is rated up to a 70 lb bag; while every website I've seen this mount for sale says its rated at a 100lbs; which is the weight of the heavy bag that I have.