In terms of running doing the bulk of my milage at 6 minute pace is giving me the best response and in terms of strength focussing on the overhead squat has taken the load off and back strength is increasing instead of breaking down as it was doing squats.
To help with positioning in the overhead squat I have been utilizing the reverse overhead squat which has been simply fantastic in setting things up for the overhead squat and the running intervals to follow.
Another great exercise I have stumbled upon is the "pull through" to increase leg and back strength without over loading the back as with the deadlift.
The take home message here is finding the correct mix of exercises to build back strength without overloading so that the strength sessions are building strength and not re-injuring. Over time as back strength increases these exercise can be replaced with more challenging ones.
As for the pace of the running, the big thing here is to push the system to improve but not to push so hard so that it slows progression so at this point doing workouts at 6minute per mile pace is increasing fitness but doing intervals at 5minute pace or faster is causing the back to spasm and slowing progression.