If you want to keep it simple and just add some weight, I got 25 ft of 3/8 inch poly rope, cut it so it was a 1/4 inch longer than the shaft length and install the poly rope thru the nock position on easton 500 size powerflight shafts.
gets the weight up to right around 500 gr at 29 1/2 inch length. does not change the spine of the shaft etc...
I do have several archers that do not add the insert weight of 50 or 100 gr weight, but they also have higher poundage long bow in the weight range of 60 to 65 lbs. they say it does not seem to make much of a difference to them, they also are using muzzy 125 gr BH....
Bill