Only thing to remember is if you can get someone to sit on the bike, therefore pre-loading the torque arm bushes, as you tighten the bolts. No great problem if you can't though (I didn't the last time I changed torque arms).
What I don't understand is the physics of it. By shortening the torque arm are you not lowering the angle of the final drive therefore "stretching" the rear shock? So causing an effect to the shock?
or am I just missing something obvious?