For a stock (or near stock) application, I would get 1-1/2" (yeah, one-HALF inch) equal length shorties. Easy to install, and really help with the low end torque.
The 1-5/8 are too big for a stock motor IMOHO, and you wont be making enough power top end to offset what you lost donw low.
I had the 1-1/2's on mine for a while, and even ran with them on my S-trim... Go small!
