Body Max 2 at 90+ min. is a great choice, Carrie!
I would also suggest Low Max. Just did that one yesterday and it's a fun step workout. It may fit the bill as it's long (70 mins.), steady state (like a long run), not toooo intense (probably working in low to middle of target heart rate zone), and it has a nice leg focus ('blasts' inserted in the workout focus on dynamic leg work but it is low impact so won't over-stress your joints).
Some other options that may work for you:
*Cathe's spin bike workouts - if you want to ramp it up, spin is great repetitive work for the legs and may increase your leg turnover rate and it also works the complementary muscles in the legs which can help break through running plateaus. Cathe's workouts all have longer premixes so you should be able to find the time frame you want. And they are basically steady state (except 2 short tabatas in the S&S Cycle Sweat which you could skip over if desired).
*X10 has a 77 minute premix if you want one of Cathe's longest workouts that gives you some killer cardio conditioning.
Best of luck on the marathon this spring, Michelle! Let us know how it goes.