Oh yeah - I forgot about your difficulties in the structure of the week. Before I answer that, I'll give you my thoughts on P&D.
This marathon was the first time I've run a negative split in my 10 marathons and I would put that down to being stronger than before (ie. more endurance). I think I can directly attribute this to the number of long and medium long runs I did. The downside of that was the training felt hard work, and plodding (like you) has never been my strong point. Consequently, half way through I felt quite stale.
I missed a number of the speed sessions and managed only three really in the whole 18 weeks. I think this proves that, at the speed we are trying to run at, endurance sessions benefit us more for the marathon.
The sessions I got most out of were the tempo runs, typically 9 miles with 4 or 5 in the middle at HMP. These were hard!!! And the LSR's with a portion at Planned MP. I usually ran the MP part at the end to mimic running at that pace on tired legs. I actually found these harder in training than I did on the day.
I have found a new love of the taper. I really think it prepared me well. I did do that 17 miler 12 days before but I think I would do that again but probably 14 days before. I did 5 mile warm up, 7 at MP and 5 warm down. It was good for confidence.
My overall feeling is that P&D has some good ideas but I didn't like following it religiously. I tried to do the 55-70 plan but abandoned it after 7 or 8 weeks.
I would do this next time. I, actually, like doing similar sessions on each day of the week, so:
Monday: Rest
Tuesday: 9 miles including 5 at Tempo (alternating with a MLR fortnightly)
Wednesday: 5 miles recovery (alternating with a MLR fortnightly)
Thursday: Intervals (eg. 6 x 800m or 4 x 1 mile)
Friday: 5 miles recovery
Saturday: rest
Sunday: LSR (with a number 5-10 at MP every other week)
I don't know if you could incorporate this into your diary. I think the MLR is probably more important than the intervals so perhaps you should try to do the tempo session and the LSR every week. I found I could do an MLR and a LSR within 2 days if I rested in between.
Would this work?:
Monday: Rest
Tuesday: MLR (11 - 16 miles)
Wednesday: 5 miles Recovery
Thursday: Tempo or recovery
Friday: tempo or recovery
Saturday: Rest
Sunday: LSR (including 5-10 at MP every other week)
I think you can get away with doing 2 of 3 key session each week. That is, 2 of MLR/LSR and Tempo.
If you want to PM me your email address we could discuss it further. I hate this view on here and can't remember what I've said! Hope this helps.