HI,
I can't comment on the differences - I've just started Sf but I know shibashi quite well and have taught it to many people - mostly those over 60 to improve flexibility, mobility, balance and general confidence in movement.
I've never taught it as a spiritual exercise and I'm interested to see the difference myself.
I've come across several versions of the shibashi movements but I use the one documented at
www.everyday-taichi.com which has full descriptions and some photo hints for anyone that wants to make the comparison for themselves.