In reply to jondo:
What distance?
I think general conditioning helps but not so much to get stronger.
Speed work I think it helps running efficiency, but I think threshold sessions are about the most important session. So 1-4 miles at around 10k > 10 mile pace, basically the speed you can run hard for an hour at. 1 min rest per mile at that same speed.
But don't ignore fairly quick medium long runs, around 10-20% off marathon pace. These really build the strength and conditioning. I'd really ignore the LSD meaning Long and Slow, its Long and Steady.
So steady consistent effort. For me that's 7:10-7:40 pace long runs but fast finish. But most aerobic gains come between 80 and 120 minutes so go that duration at least twice a week, more when building that base. Most marathoners do too many too long road runs too slowly. steady pace and fast finish at around MP in the final 6 weeks or so.