This is simple and works well.
"M" or "M-pace" equals currently achievable Marathon pace in minutes per mile. (example: M-pace for a 2:30 marathoner is 5:43m/m. So for this runner M-pace + 1 minute would be 6:43m/m)).
If you have no marathon PB, simply add 35 secs/mile to your (recent) 10k PB or 50 secs/mile to your (recent) 5km PB, and take that as your current ?M-pace?.
(Sidebar: of course this does not mean you can hop into a marathon next weekend and pop such a time. It does mean, though, that if you are as well prepared for the marathon as you were when you set these shorter distance PBs, you are capable of achieving such a marathon performance).
If you run them, all morning runs (5-6 days week, ie: every morning except Sunday and maybe one other day), start at "stumble pace", with absolutely no effort. If you feel ok, the 45 mins run might finish at M-pace + 1 minute or M-pace + 1:15 but still feel dead easy.
Afternoon/evening runs of approx 8-10 miles can begin at M + 1:15, and if you feel good can finish with 30-40 mins easily building up to M + 40 secs. Not faster.
Once per week, run an evening run of 10 miles (after 2 miles "stumble-easy" warm up) at M + 15-20 secs. Not faster.
Once per week, run an evening session of 12-15 x 1 km at exactly M-pace (not faster, even though you can) with 1 minute easy jog between them. (always include stumble-easy 2 miles to start and finish).
Sunday: one run only of 2 hr to 2:30 at M + 1 min to M + 1:15 (or slower).
An approx 70+mpw week of singles might look like this:
Mon: 6-8m @ M + 1:15/mile (alternate Mon off, especially after 2:30 sun run)
Tue: 2m warm-up: 10m @ M + 15-20secs/mile: 1m cool-down (do not do this session after the 2:30 Sun run: just jog 30 mins instead)
Wed: 6-8m @ M + 1:15/mile (or slower)
Thu: 12-14m @ M + 1:15/mile (finishing with 40 mins at M + 40 secs/mile if feeling good)
Fri: 2m warm-up: 12-15 x 1km at M-pace (not faster) with 1 min jog: 1m cool-down
Sat: 8-10m @ M + 1:15/mile (or slower)
Sun: Week 1: 1hr 45mins, Week 2: 2 hrs, Week 3; 2:30 @ M + 1 min to M + 1:15 (or slower). Week 4: Repeat from week 1)