How are you going to do that and expect it to be tight enough? Thats a BIG stretch for a shaft size oring and I'm sure your not going to break the shock down. You should be able to feel approx how much travel you use. Like Fred said you will always hit the bumper even with a very stiff setup.
Work with bump compliance and steering precision, over THE SAME section of trail.
I shouldn't write anything when dead tired
Mixed front and rear suspension in my head good night