Morning! You could probably follow a similar schedule in terms of number of runs, but you could adapt it to suit your 'non-beginner' status. Lots of set plans assume you're starting from scratch. If you've been doing a 10 mile weekend run recently, you could start in January ramping that up by 2 miles a week, so in February you're happy running 20 miles at a nice comfortable pace - nothing too quick, keep that for the weekday shorter stuff. Personally I like to get at least 5 20+ mile runs in before a marathon, done at least 2 weeks apart so don't feel you have to run 20 miles every week.
If you can do 3 midweek runs then quality is what counts. I'd suggest that one of those should be longish intervals (maybe 4 minutes fast, 2 minutes jog) at a pace you can sustain for 6 repetitions (that'll take a bit of practice!) and one should be a tempo 5 miles (not flat out, but beyond where you can have a conversation).
We might need to think about your target: if you can 'jog' 10 miles in 90 minutes when unwell then a 4 hour marathon should be well within your grasp. OTOH we want to avoid going off too fast, so we should probably set something sensible nearer the time.
