Adding that much weight to your existing full-length shafts will weaken the spine significantly. If they are currently flying well with a 125gr. head, you are likely going to have to cut them down to stiffen the spine. The good news is that with a 27″ draw length, you have some room to work with.
I would suggest taking one of your shafts and mounting the desired insert/point weight on it, and then progressively cutting in 1/2″ increments (from the rear of the arrow) until you get good flight. And hopefully it will be that simple, but only you will be able to determine that through experimentation and testing.
Keep us posted! 