3-4 day marathon training plan? (Page 2)

^^  This.

If you don't have a very solid running foundation, training for a marathon on 3-4 runs a week is an invitation to injury once you start getting up to very long weekly runs (it becomes very hard to support those runs with adequate mileage the rest of the week as you're building).  I have had one such injury (runners knee) while training for one of my marathons on that sort of schedule.

If you DO have a substantial running background (like if 30 mpw is no big deal for you going into training), it's entirely doable--I've PR'ed by more than 10 minutes twice (including a BQ) on no more than 4 runs per week, max mileage 40-50 mpw (while also maintaining cycling and swimming fitness at the Oly or HIM level).

I've never used a third-party training plan, but 4 runs sort themselves out pretty readily into an easy effort at the beginning of the week (typically that's recovery from a long run), a moderate/longer effort and a speed/power session (tempo, intervals, hills) mid-week, and a weekend long run.  I generally use a four week periodization cycle, but that's varied depending on what other races I've had going on during my marathon build.  Roughly 10% build on the long runs.