AO

It looks like the clamp has already moved back an inch or two. You might check to see if a torque tube bearing is preventing it from sliding back further. You can use a length of wire coat hanger to see if there is anything in the way. If not, use doc's suggestion and spread the clamp with a screwdriver and then slide back. If there is something in the way... then you probably need to drop the TT.

stealth

I managed to slide it back far enough; it wasn't quite sprung open enough at first and I couldn't seem to find a suitable lever to push it back...until I tried the versatile and marvelous PKBumpstick tool

stealth

The short shaft kept moving back with it, for one thing...I had to stick a thick screwdriver in the slot on the shaft to hold it forward while levering the sleeve back. The TT will have to drop to repair the housing, anyway, but looks like I can get that mess out of there now and see what tea leaves are amongst the guide tube screw shavings.