My guess is that 80-90 woudl break a 2:03/4:38 runner. they don't always correlate, for example I have friends that were so talented that they could run 31:-something for road 10k off 35 mpw. Then they increased there miles a little to 55-60 and ran 30:xx and 2:28 in the marathon. These guys tended to be 4:17-4:20 miler types in HS.
We used to joke that I ran 80 mpw over the summer and they go in shape during the warmup for the first XC meet in August.
But, I believe that if 70-80 or the 80-90 you are planning was going to be reasonable for you, you would have already been doing more miles.
You can do the "college plan" but scale down the mileage. But what you are missing here is that Summer of malmo is really the college program. Haven't read SoM in a while but I believe one of the tenets is: "I don't care how much you are running right now. However much it is run more. Find your own sweet spot."
Please look it up kids, I don't want to spread false information.