you will be fine for strength if you do that. as far as the height, if you dont like it, swap out the upper coils while there brand new still for some that are 2" shorter?
That wont net him anything unless he likes having his springs drop out and hang loosely at full extension. Typically thats not so good because they can become misaligned in their seats and mar the soft aluminum parts of the shock. He'd be better to purchase a third spring called a helper spring, which is designed solely to reduce ride height. Besides he has more than enough room on the shock to fit one of these helper springs. Thats why I sent him a 14" upper and a 16" lower. It makes room for that helper if its needed.