I find that for a rifle to point quick, you don't necessary want a shorter length of pull, but the right length of pull. Now since I've already opened my mouth, I'll tell you of my experience with a 243 with a 20 inch barrel.
Mine was a Rem 700ADL that I had the barrel cut down to 20 inches, and had a Bell and Carlson fiberglass stock installed on (much the same idea as you). The velocities where a little disappointing with the lighter bullets, and one day, I saw a coyote running across a clear cut on the snow. The shot was about 300 yards, but I figured "what the heck!" and let fly. After the shot, realizing that I'd missed by a mile, and I wasn't going to get another, I put the rifle back on my shoulder and started walking. It occurred to me that It was a lot quieter than It really should be, even my footsteps where muffled. After five minutes, my hearing came back completely, but I swore that day that if I was to have a short barreled rifle, it would be in a bit more sedate of a cartridge.
Mike