As bad as I hate to agree with arthurp[:'(][&:]
I am a firm believer in the 400 gr. "rule" myself. Also, you wouldn't have to go quite that heavy to hit 400 gr. at 26.5 inches or even 25" for that matter. I am shooting a 29 inch arrow that weighs 10.7 grains per inch and it weighs 480 grains. If you cut 4 inches off of that arrow, it would still be 437 gr. That being said, you should be able to go with an arrow weighing 9.7 - 10.0 grains, to get you to your target weight.