For a guy focusing on 8k/10k and doing 70 mpw, I think it's important to get it in singles. There are so many different ways to get there, but here is one example:
Mon: 10 miles
Tues: Longer workout, 10-12 miles total
Wed: 8 miles
Thurs: 10 miles
Fri: Shorter workout, 8 miles total
Sat: 14 mile long run
Sun: 8 miles
However, if your focus is still the 800/mile, hitting 70 with some doubles might be the better option. It's hard to give you a best structure without totally knowing who you are and your background, but here's another example:
Mon: 4 miles AM, 8 miles PM
Tues: Longer workout day, 12 miles total
Wed: 8 miles
Thurs: 4 miles AM, 8 miles PM
Fri: Shorter workout day, 8 miles total
Sat: 14 mile long run
Sun: 4 miles
Again, so many different ways to get there. Distance runners' training is so periodized throughout the year, so these are both what I would consider weeks during base training assuming 70 is as high as you want to build. From your post, I take it you're not too experienced with mileage, so that second plan would likely be better for you. Stack the miles in 6 days of the week and then take a super easy day on Sunday to recharge the batteries.
I'd encourage you to just try some different things with your training from year to year. Then you can really analyze what training works for you and build on that. Also, just because something doesn't work immediately doesn't mean it doesn't have some kind of benefit. Your body will adapt and grow from different types of training, and keeping it guessing by giving it a new stimulus is always a good thing.