I know More is MORE, and people training for a marathon all like to whip out their, uh, training logs and see who has the biggest - volume 
But, please allow me to be the exception (that proves the rule?)
You don’t have to do an insane volume of running for months and months to run a good open Mary.
I’ve done 1 70m week in my life, just to see if I could. That was many years ago.
Could count the # of 60m weeks in my lifetime on the fingers of one hand, likely with some to spare.
In '09 I did Philly as my first open Mary (having done 2 IM’s back in '06). My goal was to go < 2:50. Nice, round #.
For most of the year I’d done 25-30 mpw, w/ maybe 7-8 weeks of as much as 40 or so.
Was working with an assumed V.Dot of ~58.
Here was my last 12 weeks going into Philly (total run volume for the week, L run distance, and pace):
26, 10m, 7:01’s
26.1, 13.1m, 7:01’s (This was my Toughman HIM run)
33.8, 10m, 7:10’s
36, 13m, trail run
33, 10m, 6:45’s
34, 15m, trail run (AmZof LC - back when it was in Oct)
26, 12m, 6:56’s
47, 16m, 6:43’s
34, 8m, 6:35’s (I got an injury this week, thought I had a sfx in my foot. Turned out to be just bruised tendons, whew! But bagged the L run)
40, 20m, 6:37’s
38, 12m, 6:31’s
50, 26.2m, 6:29’s = Philly Mary 2:49:53. (* and I spent a minute+ in a porta potty, so actual ‘running time’ was 2:48:xx)
OK - looking back at this now, I have no f’n clue how I pulled that Philly time outta my ass. : )
The thing I do, which is a lot different than what pretty much anybody else’s “plan” would recommend, is run my L runs as “Steady”, not “Slow”.
I aim for an average HR of ~150 or so for the total run, and run whatever pace I can such that this is the end result.
(LTHR is ~166, give or take.) I’ve been doing this since '05, for better or worse.
My L runs end up being more like M-pace runs, plus say :00-:20/mile, depending on how I’m feeling, etc.
I don’t do hardly any Tempo running, since the L runs kinda cover that to some extent. The multisport races I did/do also kinda fill the “Tempo” box as well.
I try to mix in Strides or Pick-ups as I get closer to a race, to get my legs used to turning over quickly and smoothly.
Will occasionally do some speedwork as well, but that’s always a high-risk/moderate reward activity for me.
YMMV, and probably will.
Currently training for NYC. After totally pooching the entire month of July (avg 15 mpw - GAH!!), started getting my shit together in August.
Have done 34, 38, 35, and 46 mpw; @ 33m for this week w/ a 16m run planned for tomorrow.
Hoping to keep my weekly volume in the 50+ range from here on out, maybe even up to the 60’s by early Oct.
Dunno if this brain dump helps anybody or not, just wanted to show that you don’t necessarily need to be doing 60/70/80 mpw to break 3 hours.
Good luck!!