What adjustments are you looking for exactly? Our Level 1 plans are considered (Masters plans) and provide the reduced volume that many older athletes need – due mainly to increased recovery time needed between sessions. This volume reduction can be filled with strength training – essential for aging athletes. If the load of the Level 3 plan is not an issue – then I would say that adding strength your plan is the major adjustment I make for my masters athletes.
If I am not mistaken it appears that the Level 1 Plan maintains a periodization that has a recovery week every third week, whereas the Level 3 Plan has recovery weeks on the 4th week. Four weeks is a bit long for me as a runner in the age class. There may be some other adjustments for masters that are invisible to me.
Yes the recovery cycle is also different in the Level 1 vs Level 3 plans.
The main adjustments are focus on strength, and as becomes necessary (as its very individual) and increase in rest and recovery with a reduction in volume.